Texas Instruments | LM61460-Q1 Automotive 3-V to 36-V, 6-A, Low EMI Synchronous Step-Down Converter (Rev. C) | Datasheet | Texas Instruments LM61460-Q1 Automotive 3-V to 36-V, 6-A, Low EMI Synchronous Step-Down Converter (Rev. C) Datasheet

Texas Instruments LM61460-Q1 Automotive 3-V to 36-V, 6-A, Low EMI Synchronous Step-Down Converter (Rev. C) Datasheet
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LM61460-Q1
SNVSB70C – MAY 2019 – REVISED DECEMBER 2019
LM61460-Q1 Automotive 3-V to 36-V, 6-A, Low EMI Synchronous Step-Down Converter
1 Features
3 Description
•
The LM61460-Q1 is an automotive-focused, highperformance,
DC-DC
synchronous
step-down
converter. With integrated high-side and low-side
MOSFETs, up to 6 A of output current is delivered
over a wide input range of 3.0 V to 36 V; tolerant of
42 V, easing input surge protection design. The
LM61460-Q1 implements soft recovery from dropout
eliminating overshoot on the output.
1
•
•
•
•
AEC-Q100 qualified for automotive applications
– Temperature grade 1: –40°C to +150°C, TJ
Optimized for ultra low EMI requirements
– Meets CISPR25 class 5 standard
– Hotrod™ package minimizes switch node
ringing
– Parallel input path minimizes parasitic
inductance
– Spread spectrum reduces peak emissions
– Adjustable SW node rise time
Designed for automotive applications
– Supports 42 V automotive load dump
– ±1% total output regulation accuracy
– VOUT adjustable from 1 V to 95% of VIN
– 0.4-V dropout with 4-A load (typical)
– Protection features: thermal shutdown, input
undervoltage lockout, cycle-by-cycle current
limit, hiccup short-circuit protection
High efficiency power conversion at all loads
– 7-µA no load current at 13.5 VIN, 3.3 VOUT
– 91% PFM efficiency at 1-mA, 13.5 VIN, 5 VOUT
– External bias option for improved efficiency
Suitable for scalable power supplies
– Pin compatible with:
– LM61440-Q1 (36 V, 4 A, Adjustable fSW)
– LM62440-Q1 (36 V, 4 A, Fixed fSW)
The LM61460-Q1 is specifically designed for minimal
EMI. The device incorporates pseudo-random spread
spectrum, adjustable SW node rise time, low-EMI
VQFN-HR package featuring low switch node ringing,
and optimized pinout for ease of use. The switching
frequency can be set or synchronized between 200
kHz and 2.2 MHz to avoid noise sensitive frequency
bands. In addition the frequency can be selected for
improved efficiency at low operating frequency or
smaller solution size at high operating frequency.
Auto-mode enables frequency foldback when
operating at light loads, allowing an unloaded current
consumption of only 7 µA (typical) and high light load
efficiency. Seamless transition between PWM and
PFM modes, along with very low MOSFET ON
resistances and an external bias input, ensures
exceptional efficiency across the entire load range.
The LM61460-Q1 is qualified to automotive AECQ100 grade 1 and is available in a 14-pin VQFN-HR
package
with
wettable
flanks.
Electrical
characteristics are specified over a junction
temperature range of –40°C to +150°C.
Find
additional
Documentation.
2 Applications
•
•
Automotive infotainment and cluster: head unit,
media hub, USB charge, display
Automotive ADAS and body electronics
resources
in
the
Related
Device Information(1)
PART NUMBER
LM61460-Q1
PACKAGE
VQFN-HR (14)
BODY SIZE (NOM)
4.00 mm × 3.50 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Efficiency: VOUT = 5 V, FSW = 400 kHz
Conducted EMI: VOUT = 5 V, IOUT = 5 A
100%
95%
Efficiency (%)
90%
85%
80%
75%
70%
YELLOW: PEAK
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
BLUE: AVERAGE
65%
60%
0.0001
0.001
0.01
0.1 0.2 0.5 1
Load Current (A)
2 3 5 710
LM61
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM61460-Q1
SNVSB70C – MAY 2019 – REVISED DECEMBER 2019
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Comparison Table.....................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
2
3
4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
4
4
4
5
5
7
8
9
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Characteristics...............................................
Systems Characteristics............................................
Typical Characteristics ..............................................
Detailed Description ............................................ 11
8.1 Overview ................................................................. 11
8.2 Functional Block Diagram ....................................... 12
8.3 Feature Description................................................. 13
8.4 Device Functional Modes........................................ 22
9
Application and Implementation ........................ 28
9.1 Application Information............................................ 28
9.2 Typical Application ................................................. 28
10 Power Supply Recommendations ..................... 43
11 Layout................................................................... 44
11.1 Layout Guidelines ................................................. 44
11.2 Layout Example .................................................... 46
12 Device and Documentation Support ................. 47
12.1
12.2
12.3
12.4
12.5
12.6
Documentation Support .......................................
Receiving Notification of Documentation Updates
Support Resources ...............................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
47
47
47
47
47
47
13 Mechanical, Packaging, and Orderable
Information ........................................................... 47
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (December 2019) to Revision C
•
Page
Changed device status from Advance Information to Production Data ................................................................................. 1
Changes from Revision A (September 2019) to Revision B
Page
•
Added Typical Characteristics ................................................................................................................................................ 9
•
Added Application Curves ................................................................................................................................................... 34
Changes from Original (May 2019) to Revision A
Page
•
First public release ................................................................................................................................................................ 1
•
Changed standby current from 9-µA to 7-µA in the Features ................................................................................................ 1
•
Updated Device Comparison Table ....................................................................................................................................... 2
•
Edited EN/SYNC Uses for Enable and VIN UVLO ............................................................................................................... 13
•
Edited EN/SYNC Pin Uses for Synchronization ................................................................................................................... 13
5 Device Comparison Table
DEVICE
LM61460-Q1
2
ORDERABLE PART
NUMBER
REFERENCE PART
NUMBER
LIGHT LOAD
MODE
SPREAD
SPECTRUM
OUTPUT
VOLTAGE
SWITCHING
FREQUENCY
LM61460AANQRJRTQ1
LM61460AAN-Q1
Auto Mode
No
Adjustable
Adjustable
LM61460AASQRJRTQ1
LM61460AAS-Q1
Auto Mode
Yes
Adjustable
Adjustable
LM61460AFSQRJRTQ1
LM61460AFS-Q1
FPWM
Yes
Adjustable
Adjustable
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SNVSB70C – MAY 2019 – REVISED DECEMBER 2019
6 Pin Configuration and Functions
CBOOT
RBOOT
VIN2
13
12
1
5
11
PGND2
10
SW
9
8
PGOOD
VIN1
4
7
FB
6
2
3
RT
VCC
AGND
EN/
SYNC
BIAS
14
RJR Package
14-Pin VQFN-HR
Top View
PGND1
Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
BIAS
1
P
Input to internal LDO. Connect to output voltage point to improve efficiency. Connect an
optional high quality 0.1-µF to 1-µF capacitor from this pin to ground for improved noise
immunity. If output voltage is above 12 V, connect this pin to ground.
VCC
2
O
Internal LDO output. Used as supply to internal control circuits. Do not connect to any
external loads. Connect a high-quality 1-µF capacitor from this pin to AGND.
AGND
3
G
Analog ground for internal circuitry. Feedback and VCC are measured with respect to this
pin. Must connect AGND to both PGND1 and PGND2 on PCB.
FB
4
I
Output voltage feedback input to the internal control loop. Connect to feedback divider tap
point for adjustable output voltage. Do not float or connect to ground.
PGOOD
5
O
Open-drain power-good status output. Pull this pin up to a suitable voltage supply through a
current limiting resistor. High = power OK, low = fault. PGOOD output goes low when EN =
low, VIN > 1-V.
RT
6
I/O
Connect this pin to ground through a resistor with value between 5.76 kΩ and 66.5 kΩ to set
switching frequency between 200 kHz and 2200 kHz. Do not float or connect to ground.
EN/SYNC
7
I
Precision enable input. High = on, Low = off. Can be connected to VIN. Precision enable
allows the pin to be used as an adjustable UVLO. See the Application and Implementation
section. Do not float. EN/SYNC also functions as a synchronization input pin. Triggers on
rising edge of external clock. A capacitor must be used to AC couple the synchronization
signal to this pin. When synchronized to external clock, the device functions in forced PWM
and disables the PFM light load efficiency mode. See the Detailed Description.
VIN1
8
P
Input supply to the converter. Connect a high-quality bypass capacitor or capacitors from this
pin to PGND1. Low impedance connection must be provided to VIN2.
PGND1
9
G
Power ground to internal low side MOSFET. Connect to system ground. Low impedance
connection should be provided to PGND2. Connect a high-quality bypass capacitor or
capacitors from this pin to VIN1.
SW
10
O
Switch node of the converter. Connect to output inductor.
PGND2
11
G
Power ground to internal low side MOSFET. Connect to system ground. Low impedance
connection must be provided to PGND1. Connect a high-quality bypass capacitor or
capacitors from this pin to VIN2.
VIN2
12
P
Input supply to the converter. Connect a high quality bypass capacitor or capacitors from this
pin to PGND2. Low impedance connection must be provided to VIN1.
RBOOT
13
I/O
Connect to CBOOT through a resistor. This resistance must be between 0 Ω and open and
determines SW node rise time.
CBOOT
14
I/O
High-side driver upper supply rail. Connect a 100-nF capacitor between SW pin and CBOOT.
An internal diode connects to VCC and allows CBOOT to charge while SW node is low.
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7 Specifications
7.1 Absolute Maximum Ratings
Over the recommended operating junction temperature range of -40℃ to +150℃ (unless otherwise noted) (1)
Input Voltage
PARAMETER
MIN
MAX
VIN1, VIN2 to AGND, PGND
-0.3
42
V
RBOOT to SW
-0.3
5.5
V
CBOOT to SW
-0.3
5.5
V
BIAS to AGND, PGND
-0.3
16
V
EN/SYNC to AGND, PGND
-0.3
42
V
RT to AGND, PGND
-0.3
5.5
V
FB to AGND, PGND
-0.3
16
V
PGOOD to AGND, PGND
0
20
V
-1
2
V
SW to AGND, PGND (3)
-0.3
VIN+0.3
V
VCC to AGND, PGND
-0.3
5.5
V
PGND to AGND (2)
Output Voltage
UNIT
(4)
Current
PGOOD sink current
10
mA
TJ
Junction temperature
-40
150
°C
Tstg
Storage temperature
-40
150
°C
(1)
(2)
(3)
(4)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
This specification applies to voltage durations of 100 ns or less. The maximum D.C. voltage should not exceed ± 0.3 V.
A voltage of 2 V below GND and 2 V above VIN can appear on this pin for ≤ 200 ns with a duty cycle of ≤ 0.01%.
Do not exceed pin’s voltage rating.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
Electrostatic discharge
Human body model (HBM), per AEC Q100-002 (1)
Device HBM Classification Level 2
±2000
Charged device model (CDM), per AEC Q100-011
Device CDM Classification Level C5
±750
UNIT
V
AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
7.3 Recommended Operating Conditions
Over the recommended operating junction temperature range of -40°C to 150°C (unless otherwise noted)
MIN
Input voltage
Input voltage range after start-up
Output voltage
Output voltage range for adjustable version
Frequency
Sync frequency
36
0.95 * VIN
Frequency adjustment range
200
2200
kHz
Synchronization frequency range
200
2200
kHz
Operating junction temperature TJ range
4
(2)
(3)
Output DC current range
(4)
UNIT
1
Temperature
(2)
(3)
MAX
3
Load current
(1)
NOM
(1)
(4)
V
V
0
6
A
–40
150
°C
Recommended operating conditions indicate conditions for which the device is intended to be functional, but do not ensure specific
performance limits. For ensured specifications, see Electrical Characteristics table.
Under no conditions should the output voltage be allowed to fall below zero volts.
Maximum continuous DC current may be derated when operating with high switching frequency and/or high ambient temperature. See
Application section for details.
High junction temperatures degrade operating lifetimes. Operating lifetime is de-rated for junction temperatures greater than 125℃.
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7.4 Thermal Information
The value of RθJA given in this table is only valid for comparison with other packages and cannot be used for design purposes.
These values were calculated in accordance with JESD 51-7, and simulated on a 4-layer JEDEC board. They do not
represent the performance obtained in an actual application. For example, with a 4-layer PCB, a RΘJA = 25℃/W can be
achieved. For design information see Maximum Ambient Temperature versus Output Current.
LM61460-Q1
THERMAL METRIC
(1) (2)
RJR (QFN)
UNIT
14 PINS
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
Junction-to-case (top) thermal resistance
RθJB
Junction-to-board thermal resistance
ΨJT
Junction-to-top characterization parameter
1.4
°C/W
ΨJB
Junction-to-board characterization parameter
19
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
-
°C/W
(1)
(2)
59
°C/W
19
°C/W
19.2
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
The value of RθJA given in this table is only valid for comparison with other packages and cannot be used for design purposes. These
values were calculated in accordance with JESD 51-7, and simulated on a 4-layer JEDEC board. They do not represent the
performance obtained in an actual application.
7.5 Electrical Characteristics
Limits apply over the recommended operating junction temperature range of -40°C to +150°C, unless otherwise stated.
Minimum and Maximum limits are specified through test, design or statistical correlation. Typical values represent the most
likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following
conditions apply: VIN = 13.5 V. VIN1 shorted to VIN2 = VIN. VOUT is converter output voltage.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNIT
SUPPLY VOLTAGE AND CURRENT
Needed to start up
VIN_OPERATE
Input operating voltage (1)
VIN_OPERATE_H
Hysteresis (1)
IQ
Operating quiescent current (not
switching); measured at VIN pin (2)
IBIAS
ISD
Once operating
3.95
V
3.0
1
VFB = +5%, VBIAS = 5 V
V
0.6
6
µA
Current into BIAS pin (not switching,
VFB = +5%, VBIAS = 5 V, Auto Mode
maximum at TJ = 125°C) (2)
24
31.2
µA
Shutdown quiescent current;
measured at VIN pin
0.6
6
µA
EN = 0 V, TJ = 25℃
ENABLE
VEN
Enable input threshold voltage rising
VEN-ACC
Enable input threshold voltage rising deviation from typical
VEN-HYST
Enable threshold hysteresis as
percentage of VEN (TYP)
VEN-WAKE
Enable wake-up threshold
IEN
Enable pin input current
VIN = EN = 13.5 V
VEN_SYNC
Edge height necessary to sync
using EN/SYNC pin
Rise/fall time <30 ns
1.263
-8.1
24
28
V
8.1
%
32
%
0.4
V
2.3
µA
2.4
V
LDO - VCC
VCC
(1)
(2)
Internal VCC voltage
VBIAS > 3.4 V, CCM Operation (1)
3.3
VBIAS = 3.1 V, Non-switching
3.1
V
Parameter specified by design, statistical analysis and production testing of correlated parameters.
This is the current used by the device while not switching, open loop, with FB pulled to +5% of nominal. It does not represent the total
input current to the system while regulating. For additional information, reference the Systems Characteristics Table and the Input
Supply Current Section.
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Electrical Characteristics (continued)
Limits apply over the recommended operating junction temperature range of -40°C to +150°C, unless otherwise stated.
Minimum and Maximum limits are specified through test, design or statistical correlation. Typical values represent the most
likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following
conditions apply: VIN = 13.5 V. VIN1 shorted to VIN2 = VIN. VOUT is converter output voltage.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNIT
VCC_UVLO
Internal VCC input under voltage
lock-out
VCC rising under voltage threshold
3.6
V
VCC_UVLO_HYST
Internal VCC input under voltage
lock-out
Hysteresis below VCC_UVLO
1.1
V
FEEDBACK
VFB_acc
Initial reference voltage accuracy for
VIN = 3.3 V to 36 V, TJ = 25℃,
5-V, 3.3-V and adjustable (1 V FB)
FPWM Mode
versions
IFB
Input current from FB to AGND
Adjustable versions only, FB = 1 V
Minimum adjustable frequency by
RT or SYNC
RT = 66.5 kΩ
0.18
0.2
0.22 MHz
Adjustable frequency by RT or
SYNC with 400 kHz setting
RT = 33.2 kΩ
0.36
0.4
0.44 MHz
Maximum adjustable frequency
by RT or SYNC
RT = 5.76 kΩ
1.98
2.2
2.42 MHz
-1
1
%
10
nA
OSCILLATOR
fADJ
fSSS
Frequency span of spread spectrum
operation - largest deviation from
Spread spectrum active
center frequency
fPSS
Spread spectrum pattern
frequency (1)
Spread spectrum active, fSW = 2.1
MHz
RDS(ON)_HS
Power switch on-resistance
High side MOSFET RDS(ON)
RDS(ON)_LS
Power switch on-resistance
Low side MOSFET RDS(ON)
VBOOT_UVLO
Voltage on CBOOT pin compared to
SW which will turn off high-side
switch
2
%
1.5
Hz
41
82
mΩ
21
45
mΩ
MOSFETS
2.1
V
CURRENT LIMITS
IL-HS
High side switch current limit (3)
IL-LS
Low side switch current limit
IL-ZC
Zero-cross current limit. Positive
current direction is out of SW pin
Auto Mode, static measurement
IL-NEG
Negative current limit FPWM and
SYNC Modes. Positive current
direction is out of SW pin.
IPK_MIN_0
Duty Cycle approaches 0%
8.9
10.3
11.5
A
6.1
7.1
8.1
A
0.25
A
FPWM operation
-3
A
Minimum peak command in Auto
Mode / device current rating
Pulse duration < 100 ns
25
%
IPK_MIN_100
Minimum peak command in Auto
Mode / device current rating
Pulse duration > 1 µs
12.5
%
VHICCUP
Ratio of FB voltage to in-regulation
FB voltage
Not during soft start
40
%
PGDOV
PGOOD upper threshold - rising
% of VOUT setting
105
107
110
%
PGDUV
PGOOD lower threshold - falling
% of VOUT setting
92
94
96.5
%
PGDHYST
PGOOD upper threshold (rising &
falling)
% of VOUT setting
VIN(PGD_VALID)
Input voltage for proper
PGOOD function
POWER GOOD
(3)
6
1.3
1.0
%
V
High side current limit is a function of duty factor. High side current limit value is highest at small duty factor and less at higher duty
factors.
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Electrical Characteristics (continued)
Limits apply over the recommended operating junction temperature range of -40°C to +150°C, unless otherwise stated.
Minimum and Maximum limits are specified through test, design or statistical correlation. Typical values represent the most
likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following
conditions apply: VIN = 13.5 V. VIN1 shorted to VIN2 = VIN. VOUT is converter output voltage.
PARAMETER
VPGD(LOW)
RPGD
TEST CONDITIONS
Low level PGOOD function output
voltage
RDS(ON) of PGOOD output
MIN
MAX UNIT
0.4
1 mA pullup to PGOOD pin, VIN =
13.5 V, EN = 0 V
0.4
2 mA pullup to PGOOD pin, VIN =
13.5 V, EN = 3.3 V
0.4
V
1 mA pullup to PGOOD pin, EN = 0
V
17
40
Ω
1 mA pullup to PGOOD pin, EN =
3.3 V
40
90
Ω
Pull down current at the SW node
under over voltage condition
IOV
TYP
46 µA pullup to PGOOD pin, VIN =
1.0 V, EN = 0 V
0.5
mA
THERMAL SHUTDOWN
TSD_R
TSD_HYST
Thermal shutdown rising
threshold (1)
Thermal shutdown hysteresis
158
(1)
168
180
℃
℃
10
7.6 Timing Characteristics
Limits apply over the recommended operating junction temperature range of -40°C to +150°C, unless otherwise stated.
Minimum and Maximum limits are specified through test, design or statistical correlation. Typical values represent the most
likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise stated the following
conditions apply: VIN = 13.5 V.
Parameter
Test Condition
MIN
TYP
MAX UNIT
SWITCH NODE
tON_MIN
Minimum HS switch on time
tON_MAX
Maximum HS switch on time
VIN = 20 V, IOUT = 2 A, RBOOT
short to CBOOT
55
70
9
tOFF_MIN
Minimum LS switch on time
VIN = 4.0 V, IOUT = 1 A, RBOOT
short to CBOOT
tSS
Time from first SW pulse to VREF at
90%
VIN ≥ 4.2 V
tSS2
Time from first SW pulse to release
of FPWM lockout if output not in
regulation
VIN ≥ 4.2 V
tW
Short circuit wait time ("Hiccup"
time)
ns
μs
65
85
ns
3.5
5
7
ms
9.5
13
17
ms
80
ms
0.7
ms
ENABLE
CVCC = 1 µF, time from EN high to
first SW pulse if output starts at 0 V
tEN
Turn-on delay (1)
tB
Blanking of EN after rising or falling
edges (1)
tSYNC_EDGE
Enable sync signal hold time after
edge for edge recognition
100
tPGDFLT(rise)
Delay time to PGOOD high signal
1.5
tPGDFLT(fall)
Glitch filter time constant for
PGOOD function
4
28
µs
ns
POWER GOOD
(1)
2
2.5
120
ms
µs
Parameter specified using design, statistical analysis and production testing of correlated parameters; not tested in production.
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7.7 Systems Characteristics
The following values are specified by design provided that the component values in the typical application circuit are used.
Limits apply over the junction temperature range of -40°C to +150°C, unless otherwise noted. Minimum and Maximum limits
are derived using test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C,
and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VIN = 13.5 V. VIN1
shorted to VIN2 = VIN. VOUT is output setting. These parameters are not tested in production.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX UNIT
EFFICIENCY
ƞ5V_2p1MHz
ƞ3p3V_2p1MHz
ƞ5V_400kHz
Typical 2.1 MHz efficiency
Typical 2.1 MHz efficiency
Typical 400 kHz efficiency
VOUT = 5 V, IOUT = 4 A, RBOOT = 0 Ω
93
VOUT = 5 V, IOUT = 100 µA,
RBOOT = 0 Ω, RFBT = 1 MΩ
73
VOUT = 3.3 V, IOUT = 4 A,
RBOOT = 0 Ω
91
VOUT = 3.3 V, IOUT = 100 µA,
RBOOT = 0 Ω, RFBT = 1 MΩ
71
VOUT = 5 V, IOUT = 4 A, RBOOT = 0 Ω
95
VOUT = 5 V, IOUT = 100 µA,
RBOOT = 0 Ω, RFBT = 1 MΩ
76
%
%
%
RANGE OF OPERATION
VVIN_MIN1
VIN for full functionality at reduced
load, after start-up.
VOUT set to 3.3 V
3.0
V
VVIN_MIN2
VIN for full functionality at 100% of
maximum rated load, after start-up.
VOUT set to 3.3 V
3.95
V
IQ-VIN
Operating quiescent current
VOUT = 3.3 V, IOUT = 0 A, Auto
mode, RFBT=1 MΩ
(1)
7
µA
VOUT = 5 V, IOUT = 0 A, Auto mode,
RFBT=1 MΩ
10
VOUT = 3.3 V, IOUT = 4 A, -3% output
Input to output voltage differential to accuracy at 25℃
maintain regulation accuracy without
VOUT = 3.3 V, IOUT = 4 A, -3% output
inductor DCR drop
accuracy at 125℃
VDROP1
Input to output voltage differential to
maintain fSW ≥ 1.85MHz, without
DCR drop
VDROP2
DMAX
Maximum switch duty cycle
0.4
V
0.55
VOUT = 3.3 V, IOUT = 4 A, -3%
regulation accuracy at 25℃
0.8
VOUT = 3.3 V, IOUT = 4 A, -3%
regulation accuracy at 125℃
1.2
fSW =1.85 MHz
87
While in frequency fold back
V
98
%
%
RBOOT
tRISE
(1)
8
SW node rise time
RBOOT = 0 Ω, IOUT = 2 A (10% to
80%)
RBOOT = 100 Ω, IOUT = 2 A (10% to
80%)
2.15
ns
2.7
ns
See detailed description for the meaning of this specification and how it can be calculated.
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7.8 Typical Characteristics
Unless otherwise specified, VIN = 13.5 V and fSW = 400 kHz.
4000
1.5
1.25
Shutdown Current (nA)
Quiescent Current (µA)
3500
1
0.75
3000
2500
2000
1500
1000
-40C
25C
150C
500
0.5
-50
0
-25
0
25
50
75
Temperature (°C)
100
125
0
150
5
10
SNVS
VFB = 1 V
15
20
25
Input Voltage (V)
30
35
40
SNVS
VEN = 0 V
Figure 1. Non-Switching Input Supply Current
Figure 2. Shutdown Supply Current
11
1.01
10
1.006
Current (A)
Voltage (V)
9
1.002
0.998
8
7
0.994
6
0.99
-50
-25
0
25
50
75
Temperature (°C)
100
125
5
-50
150
0
25
50
75
Temperature (°C)
100
125
150
SNVS
Figure 4. LM61460-Q1 High Side and Low Side Current
Limits
70
FREQ = 200 kHz
FREQ = 400 kHz
FREQ = 2.2 MHz
60
RDS-ON (m-Ohm)
Frequency (kHz)
-25
snvs
Figure 3. Feedback Voltage
3500
3250
3000
2750
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
-50
HS
LS
50
40
30
20
-25
0
25
50
75
Temperature (°C)
100
125
150
HS Switch
LS Switch
10
-50
-25
SNVS
Figure 5. Switching Frequency Set by RT Resistor
0
25
50
75
Temperature (°C)
100
125
150
SNVS
Figure 6. High Side and Low Side Switches RDS_ON
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Typical Characteristics (continued)
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-50
115
110
PGOOD Threshold (%)
Enable Threshold (V)
Unless otherwise specified, VIN = 13.5 V and fSW = 400 kHz.
VEN Rising
VEN Falling
VEN_WAKE Rising
VEN_WAKE Falling
-25
0
25
50
75
Temperature (°C)
100
125
105
100
95
90
OV Tripping
OV Recovery
UV Recovery
UV Tripping
85
150
80
-50
-25
snvs
Figure 7. Enable Thresholds
10
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0
25
50
75
Temperature (°C)
100
125
150
SNVS
Figure 8. PGOOD Thresholds
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8 Detailed Description
8.1 Overview
The LM61460-Q1 is a wide input, synchronous peak-current mode buck regulator designed for a wide variety of
automotive applications. The regulator can operate over a wide range of switching frequencies including sub-AM
band at 400 kHz and above the AM band at 2.1 MHz. This device operates over a wide range of conversion
ratios. If minimum on-time or minimum off-time does not support the desired conversion ratio, frequency is
reduced automatically, allowing output voltage regulation to be maintained during input voltage transients with a
high operating-frequency setting.
The LM61460-Q1 has been designed for low EMI and is optimized for both above and below AM band operation:
• Meets CISPR25 class 5 standard
• Hotrod™ package minimizes switch node ringing
• Parallel input path minimizes parasitic inductance
• Spread spectrum reduces peak emissions
• Adjustable SW node rise time
These features together can eliminate shielding and other expensive EMI mitigation measures.
This device is designed to minimize end-product cost and size while operating in demanding automotive
environments. Operation at 2.1 MHz allows for the use of small passive components. State of the art current limit
function allow the use of inductors that are optimized for 4-A and 6-A regulators. In addition, this device has low
unloaded current consumption, desirable for off-battery, always on applications. The low shutdown current and
high maximum operating voltage also allows for the elimination of an external load switch and input transient
protection. To further reduce system cost, an advanced PGOOD output is provided, which can often eliminate
the use of an external reset or supervisory device.
The LM61460-Q1 devices are AEC-Q100 qualified and have electrical characteristics guaranteed up to a
maximum junction temperature of 150°C.
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8.2 Functional Block Diagram
VCC
Clock
VCC
Oscillator
RT
BIAS
VCC UVLO
Slope
compensation
SYNC
Detect
LDO
Over
Temperature
detect
Sync
Frequency Foldback
FPWM/Auto
RBOOT
System enable
Enable
EN/SYNC
VIN
OTP
CBOOT
HS Current
sense
Error
amplifier
±
VIN
System enable
OTP
Hiccup active
Soft start
circuit and
bandgap
VCC UVLO
AGND
VIN2
Clock
High and
low limiting
circuit
Output
low
FB
+
+
±
Comp Node
+
VIN1
+
HS
Current
Limit
±
SW
Drivers and
logic
LS
Current
Limit
±
+
Voltage Reference
±
FPWM/Auto
PGOOD
PGOOD
Logic with
filter and
release delay
LS
Current
Min
PGND1
+
PGND2
Vout OV
LS Current
sense
System enable
12
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8.3 Feature Description
8.3.1 EN/SYNC Uses for Enable and VIN UVLO
Start-up and shutdown are controlled by the EN/SYNC input and VIN UVLO. For the device to remain in
shutdown mode, apply a voltage below VEN_WAKE (.4 V) to the EN pin. In shutdown mode, the quiescent current
drops to 0.6 µA (typical). At a voltage above VEN_WAKE and below VEN, VCC is active and the SW node is
inactive. Once the EN voltage is above VEN, the chip begins to switch normally provided the input voltage is
above 3 V.
The EN/SYNC pin cannot be left floating. The simplest way to enable the operation is to connect the EN/SYNC
pin to VIN, this allows self-start-up of the LM61460-Q1 when VIN drives the internal VCC above its UVLO level.
However, many applications benefit from the employment of an enable divider network as shown in Figure 9,
which establishes a precision input undervoltage lockout (UVLO). This can be used for sequencing, to prevent
re-triggering the device when used with long input cables, or to reduce the occurrence of deep discharge of a
battery power source. Note that the precision enable threshold VEN has a 8.1% tolerance. Hysteresis should be
enough to prevent re-triggering. External logic output of another IC can also be used to drive the EN/SYNC pin,
allowing system power sequencing.
VIN
RENT
EN/SYNC
RENB
AGND
Figure 9. VIN UVLO Using the EN pin
Resistor values can be calculated using Equation 1. See the External UVLO section for additional information.
RENB = RENT Â
VEN
VON Å 9EN
where
•
VON is the desired typical start-up input voltage for the circuit being designed
(1)
Note that since the EN/SYNC pin can also be used as an external synchronization clock input. A blanking time,
tB, is applied to the enable logic after a clock edge is detected. Any logic change within the blanking time is
ignored. Blanking time is not applied when the device is in shutdown mode. The blanking time ranges from 4 µs
to 28 µs. To effectively disable the output, the EN/SYNC input must stay low for longer than 28 µs.
8.3.2 EN/SYNC Pin Uses for Synchronization
The LM61460-Q1 EN/SYNC pin can be used to synchronize the internal oscillator to an external clock. The
internal oscillator can be synchronized by AC coupling a positive clock edge into the EN pin, as shown in
Figure 10. It is recommended to keep the parallel combination value of RENT and RENB in the 100-kΩ range. RENT
is required for synchronization, but RENB can be left unmounted. Switching action can be synchronized to an
external clock ranging from 200 kHz to 2.2 MHz. The external clock must be off before start-up to allow proper
start-up sequencing.
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Feature Description (continued)
VIN
RENT
CSYNC
EN/SYNC
Clock
Source
RENB
AGND
AGND
Figure 10. Typical Implementation Allowing Synchronization Using the EN Pin
Referring to Figure 11 the AC-coupled voltage edge at the EN pin must exceed the SYNC amplitude threshold,
VEN_SYNC_MIN, to trip the internal synchronization pulse detector. In addition, the minimum EN/SYNC rising pulse
and falling pulse durations must be longer than tSYNC_EDGE(MIN) and shorter than the blanking time tB. A 3.3-V or
higher amplitude pulse signal coupled through a 1-nF capacitor, CSYNC, is suggested to use.
EN Voltage
VEN
tSYNC_EDGE
VEN_SYNC
0
VEN_SYNC
t
tSYNC_EDGE
Time
Figure 11. Typical SYNC/EN Waveform
After a valid synchronization signal is applied for 2048 cycles, the clock frequency abruptly changes to that of the
applied signal. Also, if the device in use has the spread-spectrum feature, the valid synchronization signal
overrides spread spectrum, turning it off, and the clock switches to the applied clock frequency.
8.3.3 Clock Locking
Once a valid synchronization signal is detected, a clock locking procedure is initiated. LM61460-Q1 devices
receive this signal over the EN/SYNC pin. After approximately 2048 pulses, the clock frequency changes to the
frequency of the synchronization signal. Note that while the frequency is adjusted suddenly, phase is maintained
so the clock cycle that lies between operation at the default frequency and at the synchronization frequency is of
intermediate length. This eliminates very long or very short pulses. Once frequency is adjusted, phase is
adjusted over a few tens of cycles so that rising synchronization edges correspond to rising SW node pulses.
See Figure 12.
14
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Feature Description (continued)
Pulse 1
Pulse 2
Pulse 3
Pulse
~2048
Pulse 4
Pulse
~2049
Pulse
~2050
Pulse
~2051
VSYNCDH
VSYNCDL
Synchronization
signal
SW Node
Spread Spectrum is on between pulse 1 and pulse 2048,
there is no change to operating frequency. At pulse 4,
the device transitions from Auto Mode to FPWM.
On approximately pulse 2048, spread
spectrum turns off
Also clock frequency matches the
synchronization signal and phase
locking begins
Phase lock achieved, Rising edges
align to within approximately 45 ns,
no spread spectrum
VIN
GND
Figure 12. Synchronization Process
8.3.4 Adjustable Switching Frequency
A resistor tied from the device RT pin to AGND is used to set operating frequency. Use Equation 2 or refer to
Figure 13 for resistor values. Note that a resistor value outside of the recommended range can cause the device
to shut down. This prevents unintended operation if RT pin is shorted to ground or left open. Do not apply a
pulsed signal to this pin to force synchronization. If synchronization is needed, refer to the EN/SYNC Pin Uses
for Synchronization section.
RRT(kΩ) = (1 / fSW(kHz) - 3.3 x 10-5) × 1.346 x 104
(2)
70
60
Rt (kOhm)
50
40
30
20
10
0
200
400
600
800 1000 1200 1400 1600 1800 2000 2200
Frequency (kHz)
RTvs
Figure 13. Setting Clock Frequency
8.3.5 PGOOD Output Operation
The PGOOD function is implemented to replace a discrete reset device, reducing BOM count and cost. The
PGOOD pin voltage goes low when the feedback voltage is outside of the specified PGOOD thresholds (see
Figure 8). This can occur in current limit and thermal shutdown, as well as while disabled and during normal
start-up. A glitch filter prevents false flag operation for short excursions of the output voltage, such as during line
and load transients. Output voltage excursions which are shorter than tPGDFLT_FALL do not trip the power-good
flag. Power-good operation can be best understood by referring to Figure 14.
The power-good output consists of an open drain NMOS; requiring an external pullup resistor to a suitable logic
supply or VOUT. When EN is pulled low, the flag output is also forced low. With EN low, power good remains valid
as long as the input voltage is ≥ 1 V (typical).
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Feature Description (continued)
Output
Voltage
Input
Voltage
Input Voltage
tPGDFLT(fall)
tPGDFLT(rise)
tPGDFLT(rise)
VPGD_HYST
tPGDFLT(fall)
tPGDFLT(fall)
tPGDFLT(fall)
VPGD_UV (falling)
VIN_OPERATE (rising)
VIN_OPERATE (falling)
VIN(PGD_VALID)
GND
< 18 V
PGOOD
PGOOD may
not be valid if
input is below
VIN(PGD_VALID)
Small glitches
do not cause
PGOOD to
signal a fault
Small glitches do not
reset tPGDFLT(rise) timer
Startup
delay
PGOOD may not
be valid if input is
below VIN(PGD_VALID)
Figure 14. PGOOD Timing Diagram (Excludes OV Events)
Table 1. Conditions That Cause PGOOD to Signal a Fault (Pull Low)
(1)
FAULT CONDITION INITIATED
FAULT CONDITION ENDS (AFTER WHICH tPGDFLT(rise) MUST PASS
BEFORE PGOOD OUTPUT IS RELEASED) (1)
VOUT < VOUT-target × PGDUV AND t > tPGDFLT(fall)
Output voltage in regulation:
VOUT-target × (PGDUV + PGDHYST) < VOUT < VOUT-target × (PGDOV PGDHYST) (See Figure 8.)
VOUT > VOUT-target × PGDOV AND t > tPGDFLT(fall)
Output voltage in regulation
TJ > TSD_R
TJ < TSD_F AND output voltage in regulation
EN < VEN Falling
EN > VEN Rising AND output voltage in regulation
VCC < VCC_UVLO - VCC_UVLO_HYST
VCC > VCC_UVLO AND output voltage in regulation
As an additional operational check, PGOOD remains low during soft start, defined as until the lesser of either full output voltage reached
or tSS2 has passed since initiation.
8.3.6 Internal LDO, VCC UVLO, and BIAS Input
The VCC pin is the output of the internal LDO used to supply the control circuits of the LM61460-Q1. The
nominal output is 3 V to 3.3 V. The BIAS pin is the input to the internal LDO. This input can be connected to
VOUT to provide the lowest possible input supply current. If the BIAS voltage is less than 3.1 V, VIN1 and VIN2
directly powers the internal LDO.
To prevent unsafe operation, VCC has a UVLO that prevents switching if the internal voltage is too low. See
VCC_UVLO and VCC_UVLO_HYST in the Electrical Characteristics table. Note that these UVLO values and the dropout
of the LDO are used to derive minimum VIN_OPERATE and VIN_OPERATE_H values.
8.3.7 Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
The driver of the Hight Side (HS) switch requires bias higher than VIN. The capacitor, CBOOT, connected
between CBOOT and SW works as a charge pump to boost voltage on the CBOOT pin to SW+VCC. A boot
diode is integrated on the LM61460-Q1 die to minimize external component count. It is recommended that a 100nF capacitor rated for 10-V or higher is used. The VBOOT_UVLO threshold (2.1 V typ) is designed to maintain
proper HS switch operation. If the CBOOT capacitor voltage drops below VBOOT_UVLO, then the device initiates a
charging sequence turning on the low-side switch before attempting to turn on the HS switch.
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8.3.8 Adjustable SW Node Slew Rate
To allow optimization of EMI with respect to efficiency, the LM61460-Q1 is designed to allow a resistor to select
the strength of the driver of the high-side FET during turn on. See Figure 15. The current drawn through the
RBOOT pin (the dotted loop) is magnified and drawn through from CBOOT (the dashed line). This current is
used to turn on the high-side power MOSEFT.
VIN
VCC
CBOOT
HS
Driver
HS FET
RBOOT
SW
LS FET
Figure 15. Simplified Circuit Showing How RBOOT Functions
With RBOOT short circuited to CBOOT, rise time is very fast. As a result SW node harmonics do not "roll off"
until above 150 MHz. A boot resistor of 100 Ω corresponds to approximately 2.7 ns SW node rise, and this 100Ω boot resistor virtually eliminates SW node overshoot. The slower rise time allows energy in SW node
harmonics to roll off near 100 MHz under most conditions. Rolling off harmonics eliminates the need for shielding
and common mode chokes in many applications. Note that rise time increases with increasing input voltage.
Noise due to stored charge is also greatly reduced with higher RBOOT resistance. Switching with slower slew
rate also decreases the efficiency.
8.3.9 Spread Spectrum
Spread spectrum is a factory option. To find which devices have spread spectrum enabled, see the Device
Comparison Table. The purpose of spread spectrum is to eliminate peak emissions at specific frequencies by
spreading these emissions across a wider range of frequencies rather than a part with fixed frequency operation.
In most systems containing the LM61460-Q1, low frequency-conducted emissions from the first few harmonics of
the switching frequency can be easily filtered. A more difficult design criterion is reduction of emissions at higher
harmonics which fall in the FM band. These harmonics often couple to the environment through electric fields
around the switch node and inductor. The LM61460-Q1 uses a ±2% spread of frequencies which can spread
energy smoothly across the FM and TV bands but is small enough to limit subharmonic emissions below the
device switching frequency. Peak emissions at the switching frequency of the part are only reduced slightly, by
less than 1 dB, while peaks in the FM band are typically reduced by more than 6 dB.
The LM61460-Q1 uses a cycle-to-cycle frequency hopping method based on a linear feedback shift register
(LFSR). This intelligent pseudo-random generator limits cycle-to-cycle frequency changes to limit output ripple.
The pseudo-random pattern repeats at less than 1.5 Hz, which is below the audio band.
The spread spectrum is only available while the clock of the LM61460-Q1 devices are free running at their
natural frequency. Any of the following conditions overrides spread spectrum, turning it off:
• The clock is slowed during dropout.
• The clock is slowed at light load in auto mode. In FPWM mode, spread spectrum is active even if there is no
load.
• At high input voltage/low output voltage ratio when the device operates at minimum on time the internal clock
is slowed disabling spread spectrum. See the Timing Characteristics section.
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The clock is synchronized with an external clock.
8.3.10 Soft Start and Recovery From Dropout
The LM61460-Q1 uses a reference based soft start that prevents output voltage overshoots and large inrush
currents during start up. Soft start is triggered by any of the following conditions:
• Power is applied to the VIN pin of the IC, releasing UVLO.
• EN is used to turn on the device.
• Recovery from a hiccup waiting period.
• Recovery from shutdown due to overtemperature protection.
Once soft start is triggered, the IC takes the following actions:
• The reference used by the IC to regulate output voltage is slowly ramped. The net result is that output voltage
takes tSS to reach 90% of its desired value.
• Operating mode is set to auto, activating diode emulation. This allows start-up without pulling output low if
there is a voltage already present on output.
These actions together provide start-up with limited inrush currents and also allow the use of larger output
capacitors and higher loading conditions that cause current to border on current limit during start-up without
triggering hiccup. See Figure 16.
EN and Output Voltages
tEN
V
tSS
If selected, FPWM
is enabled after
regulation but no
later than tSS2
VEN
VOUT Set
Point
VOUT
90% of
VOUT Set
Point
0V
tSS2
Time
t
Triggering event
tEN
EN and Output Voltages
Triggering event
V
tSS
If selected, FPWM
is enabled after
regulation but no
later than tSS2
VEN
VOUT Set
Point
VOUT
90% of
VOUT Set
Point
0V
tSS2
Time
t
Soft start works with both output voltage starting from 0 V on the left curves, or if there is already voltage on the
output, as shown on right. In either case, output voltage must reach within 10% of the desired value tSS after soft start
is initiated. During soft start, FPWM and hiccup are disabled. Both hiccup and FPWM are enabled once output
reaches regulation or tSS2, whichever happens first.
Figure 16. Soft-Start Operation
Any time the output voltage falls more than a few percent the output voltage will ramp up slowly. This condition is
called recovery from dropout and differs from soft start in three important ways:
• The reference voltage is set to approximately 1% above what is needed to achieve the existing output
voltage.
• Hiccup is allowed if output voltage is less than 0.4 times its set point. Note that during dropout regulation
itself, hiccup is inhibited.
• FPWM mode is allowed during recovery from dropout. If the output voltage were to suddenly be pulled up by
an external supply, the LM61460-Q1 can pull down on the output.
Despite being called recovery from dropout, this feature is active whenever output voltage drops to a few percent
lower than the set point. This primarily occurs under the following conditions:
• Dropout: When there is insufficient input voltage for the desired output voltage to be generated.
• Over-current: When there is an over-current event that is not severe enough to trigger hiccup.
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V
Input and Output
Voltage
VIN
Slope
the same
as during
soft start
VOUT
VOUT Set
Point
t
Time
Whether output voltage falls due to high load or low input voltage, once the condition that causes output to fall below
its set point is removed, the output climbs at the same speed as during start-up. Even though hiccup does not trigger
due to dropout, it can in principle be triggered during recovery if output voltage is below 0.4 times the output set point
for more than 128 clock cycles.
Figure 17. Recovery From Dropout
VOUT
(2 V/DIV)
IINDUCTOR
(1 A/DIV)
VIN
(5 V/DIV)
Time (2 ms/DIV)
Figure 18. Recovery From Dropout (VOUT = 5 V, IOUT = 4 A, VIN= 13.5 V to 4 V to 13.5 V)
8.3.11 Output Voltage Setting
A feedback resistor divider network between the output voltage and the FB pin is used to set output voltage level.
See Figure 19.
VOUT
RFBT
FB
RFBB
AGND
Figure 19. Setting Output Voltage of Adjustable Versions
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The LM61460-Q1 uses a 1-V reference voltage for the feedback (FB) pin. The FB pin voltage is regulated by the
internal controller to be the same as the reference voltage. The output voltage level is then set by the ratio of the
resistor divider. Equation 3 can be used to determine RFBB for a desired output voltage and a given RFBT. Usually
RFBT is between 10 kΩ and 1 MΩ. 100 kΩ is recommended for RFBT for improved noise immunity compared to 1
MΩ and reduced current consumption compared to lower resistance values.
RFBB =
RFBT
VOUT Å 1
(3)
In addition, a feedforward capacitor, CFF, connected in parallel with RFBT can be required to optimize the transient
response.
8.3.12 Overcurrent and Short Circuit Protection
The LM61460-Q1 is protected from overcurrent conditions with cycle-by-cycle current limiting on both the highside and the low-side MOSFETs.
High-side MOSFET overcurrent protection is implemented by the nature of the peak-current mode control. The
HS switch current is sensed when the HS is turned on after a short blanking time. Every switching cycle, the HS
switch current is compared to either the minimum of a fixed current set point or the output of the voltage
regulation loop minus slope compensation. Because the voltage loop has a maximum value and slope
compensation increases with duty cycle, HS current limit decreases with increased duty cycle when duty cycle is
above 35%. See Figure 20.
12
Command Current (A)
10
8
6
4
2
HS Maximum Current
Rated Maximum Output
0
0
0.2
0.4
0.6
Duty Cycle
0.8
1
FEAT
Figure 20. Maximum Current Allowed Through the HS FET - Function of Duty Cycle for LM61460-Q1
When the LS switch is turned on, the switch current is also sensed and monitored. Like the high-side device, the
low-side device turns off as commanded by the voltage control loop, low-side current limit. If the LS switch
current is higher than ILS_Limit at the end of a switching cycle, the switching cycle is extended until the LS current
reduces below the limit. The LS switch is turned off once the LS current falls below its limit, and the HS switch is
turned on again as long as at least one clock period has passed since the last time the HS device has turned on.
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SW Voltage
VSW
VIN
tON < tON_MAX
0
t
Inductor Current
Typically, tSW > Clock setting
iL
IL-HS
IOUT
IL-LS
t
0
Figure 21. Current Limit Waveforms
Since the current waveform assumes values between IL-HS and IL-LS, the maximum output current is very close to
the average of these two values. Hysteretic control is used and current does not increase as output voltage
approaches zero.
The LM61460-Q1 employs hiccup overcurrent protection if there is an extreme overload, and the following
conditions are met for 128 consecutive switching cycles:
• Output voltage is below approximately 0.4 times the output voltage set point.
• Greater than tSS2 has passed since soft start has started; see the Soft Start and Recovery From Dropout
section.
• The part is not operating in dropout, which is defined as having minimum off-time controlled duty cycle.
In hiccup mode, the device shuts itself down and attempts to soft start after tW. Hiccup mode helps reduce the
device power dissipation under severe over-current conditions and short circuits. See Figure 22.
Once the overload is removed, the device recovers as though in soft start; see Figure 23.
VOUT
(500 mV/DIV)
VOUT
(2 V/DIV)
IINDUCTOR
(2 A/DIV)
IINDUCTOR
(2 A/DIV)
Time (20 ms/DIV)
Time (20 ms/DIV)
Figure 22. Inductor Current Bursts During Hiccup
Figure 23. Short-Circuit Recovery
8.3.13 Thermal Shutdown
Thermal shutdown prevents the device from extreme junction temperatures by turning off the internal switches
when the IC junction temperature exceeds 165°C (typical). Thermal shutdown does not trigger below 158°C.
After thermal shutdown occurs, hysteresis prevents the device from switching until the junction temperature
drops to approximately 155°C. When the junction temperature falls below 155°C (typical), the LM61460-Q1
attempts to soft start.
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While the LM61460-Q1 is shut down due to high junction temperature, power continues to be provided to VCC.
To prevent overheating due to a short circuit applied to VCC, the LDO that provides power for VCC has reduced
current limit while the part is disabled due to high junction temperature. The VCC current limit is reduced to a few
milliamperes during thermal shutdown.
8.3.14 Input Supply Current
The LM61460-Q1 is designed to have very low input supply current when regulating light loads. This is achieved
by powering much of the internal circuitry from the output. The BIAS pin is the input to the LDO that powers the
majority of the control circuits. By connecting the BIAS input pin to the output of the regulator, a small amount of
current drawn from the output. This current is reduced at the input by the ratio of VOUT / VIN.
Output Voltage
IQ _ VIN IQ IEN IBIAS Idiv
Keff u Input Voltage
where
•
•
•
•
•
•
IQ_VIN is the current consumed by the operating (switching) buck converter while unloaded.
IQ is the current drawn from the VIN terminal. See IQ in the Electrical Characteristics.
IEN is current drawn by the EN terminal. Include this current if EN is connected to VIN. See IEN in the Electrical
Characteristics. Note that this current drops to a very low value if connected to a voltage less than 5 V.
IBIAS is bias current drawn by the BIAS input. See IBIAS in the Electrical Characteristics.
Idiv is the current drawn by the feedback voltage divider used to set output voltage.
ηeff is the light load efficiency of the buck converter with IQ_VIN removed from the input current of the buck
converter. ηeff = 0.8 is a conservative value that can be used under normal operating conditions.
(4)
8.4 Device Functional Modes
8.4.1 Shutdown Mode
The EN pin provides electrical ON and OFF control of the device. When the EN pin voltage is below 0.4 V, both
the converter and the internal LDO have no output voltage and the part is in shutdown mode. In shutdown mode,
the quiescent current drops to typically 0.6 µA.
8.4.2 Standby Mode
The internal LDO has a lower EN threshold than the output of the converter. When the EN pin voltage is above
1.1 V (maximum) and below the precision enable threshold for the output voltage, the internal LDO regulates the
VCC voltage at 3.3 V typical. The precision enable circuitry is ON once VCC is above its UVLO. The internal
power MOSFETs of the SW node remain off unless the voltage on EN pin goes above its precision enable
threshold. The LM61460-Q1 also employs UVLO protection. If the VCC voltage is below its UVLO level, the
output of the converter is turned off.
8.4.3 Active Mode
The LM61460-Q1 is in active mode whenever the EN pin is above VEN, VIN is high enough to satisfy VIN_OPERATE,
and no other fault conditions are present. The simplest way to enable the operation is to connect the EN pin to
VIN which allows self start-up when the applied input voltage exceeds the minimum VIN_OPERATE.
In active mode, depending on the load current, input voltage, and output voltage, the LM61460-Q1 is in one of
six modes:
• Continuous conduction mode (CCM) with fixed switching frequency when load current is above half of the
inductor current ripple.
• Auto Mode - Light Load Operation: PFM when switching frequency is decreased at very light load.
• FPWM Mode - Light Load Operation: Discontinuous conduction mode (DCM) when the load current is lower
than half of the inductor current ripple.
• Minimum on-time: At high input voltage, low output voltages the switching frequency is reduced to maintain
regulation.
• Dropout mode: When switching frequency is reduced to minimize voltage drop out.
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Device Functional Modes (continued)
8.4.3.1 CCM Mode
The following operating description of the LM61460-Q1 refers to the Functional Block Diagram and to the
waveforms in Figure 24. In CCM, the LM61460-Q1 supplies a regulated output voltage by turning on the internal
high-side (HS) and low-side (LS) NMOS switches with varying duty cycle (D). During the HS switch on-time, the
SW pin voltage, VSW, swings up to approximately VIN, and the inductor current, iL, increases with a linear slope.
The HS switch is turned off by the control logic. During the HS switch off-time, tOFF, the LS switch is turned on.
Inductor current discharges through the LS switch, which forces the VSW to swing below ground by the voltage
drop across the LS switch. The converter loop adjusts the duty cycle to maintain a constant output voltage. D is
defined by the on-time of the HS switch over the switching period:
D = TON / TSW
(5)
In an ideal buck converter where losses are ignored, D is proportional to the output voltage and inversely
proportional to the input voltage:
D = VOUT / VIN
(6)
SW Voltage
VSW
D=
VIN
tON
VOUT
§
tSW
VIN
tOFF
tON
0
- IOUTÂ5DSLS
t
tSW
Inductor Current
iL
ILPK
IOUT
Iripple
0
t
Figure 24. SW Voltage and Inductor Current Waveforms in Continuous Conduction Mode (CCM)
8.4.3.2 Auto Mode - Light Load Operation
The LM61460-Q1 can have two behaviors while lightly loaded. One behavior, called auto mode operation, allows
for seamless transition between normal current mode operation while heavily loaded and highly efficient light
load operation. The other behavior, called FPWM Mode, maintains full frequency even when unloaded. Which
mode the LM61460-Q1 operates in depends on which factory option is employed, see the Device Comparison
Table. Note that all parts operate in FPWM mode when synchronizing frequency to an external signal.
In auto mode, light load operation is employed in the LM61460-Q1 at load lower than approximately a tenth of
the rated maximum output current. Light-load operation employs two techniques to improve efficiency:
• Diode emulation, which allows DCM operation
• Frequency reduction
Note that while these two features operate together to create excellent light load behavior, they operate
independently of each other.
8.4.3.2.1 Diode Emulation
Diode emulation prevents reverse current though the inductor which requires a lower frequency needed to
regulate given a fixed peak inductor current. Diode emulation also limits ripple current as frequency is reduced.
With a fixed peak current, as output current is reduced to zero, frequency must be reduced to near zero to
maintain regulation.
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Device Functional Modes (continued)
VOUT
tON
<
VIN
tSW
D=
VSW
SW Voltage
VIN
tON
tOFF
tHIGHZ
0
t
tSW
Inductor Current
iL
ILPK
IOUT
0
t
In auto mode, the low-side device is turned off once SW node current is near zero. As a result, once output current is
less than half of what inductor ripple would be in CCM, the part operates in DCM which is equivalent to the statement
that diode emulation is active.
Figure 25. PFM Operation
The LM61460-Q1 has a minimum peak inductor current setting while in auto mode. Once current is reduced to a
low value with fixed input voltage, on-time is constant. Regulation is then achieved by adjusting frequency. This
mode of operation is called PFM mode regulation.
8.4.3.2.2 Frequency Reduction
The LM61460-Q1 reduces frequency whenever output voltage is high. This function is enabled whenever Comp,
an internal signal, is low and there is an offset between the regulation set point of FB and the voltage applied to
FB. The net effect is that there is larger output impedance while lightly loaded in auto mode than in normal
operation. Output voltage must be approximately 1% high when the part is completely unloaded.
Output Voltage
VOUT
Current
Limit
1% Above
Set point
VOUT Set
Point
0
Output Current
IOUT
In auto mode, once output current drops below approximately 1/10th the rated current of the part, output resistance
increases so that output voltage is 1% high while the buck is completely unloaded.
Figure 26. Steady State Output Voltage versus Output Current in Auto Mode
In PFM operation, a small DC positive offset is required on the output voltage to activate the PFM detector. The
lower the frequency in PFM, the more DC offset is needed on VOUT. If the DC offset on VOUT is not acceptable, a
dummy load at VOUT or FPWM Mode can be used to reduce or eliminate this offset.
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Device Functional Modes (continued)
8.4.3.3 FPWM Mode - Light Load Operation
Like auto mode operation, FPWM mode operation during light load operation is selected as a factory option.
In FPWM Mode, frequency is maintained while lightly loaded. To maintain frequency, a limited reverse current is
allowed to flow through the inductor. Reverse current is limited by reverse current limit circuitry, see the Electrical
Characteristics for reverse current limit values.
VSW
D=
SW Voltage
VIN
tON
VOUT
§
tSW
VIN
tOFF
tON
0
t
Inductor Current
tSW
iL
ILPK
IOUT
0
Iripple
t
In FPWM mode, Continuous Conduction (CCM) is possible even if IOUT is less than half of Iripple.
Figure 27. FPWM Mode Operation
For all devices, in FPWM mode, frequency reduction is still available if output voltage is high enough to
command minimum on-time even while lightly loaded, allowing good behavior during faults which involve output
being pulled up.
8.4.3.4 Minimum On-time (High Input Voltage) Operation
The LM61460-Q1 continues to regulate output voltage even if the input-to-output voltage ratio requires an ontime less than the minimum on-time of the chip with a given clock setting. This is accomplished using valley
current control. At all times, the compensation circuit dictates both a maximum peak inductor current and a
maximum valley inductor current. If for any reason, valley current is exceeded, the clock cycle is extended until
valley current falls below that determined by the compensation circuit. If the converter is not operating in current
limit, the maximum valley current is set above the peak inductor current, preventing valley control from being
used unless there is a failure to regulate using peak current only. If the input voltage to output voltage ratio is too
high, even though current exceeds the peak value dictated by compensation, the high-side device cannot be
turned off quickly enough to regulate output voltage. As a result, the compensation circuit reduces both peak and
valley current. Once a low enough current is selected by the compensation circuit, valley current matches that
being commanded by the compensation circuit. Under these conditions, the low-side device is kept on and the
next clock cycle is prevented from starting until inductor current drops below the desired valley current. Since ontime is fixed at its minimum value, this type of operation resembles that of a device using a COT control scheme;
see Figure 28.
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Device Functional Modes (continued)
SW Voltage
VSW
D=
VIN
tON
VOUT
§
tSW
VIN
tON = tON_MIN
tOFF
0
- IOUTÂ5DSLS
t
Inductor Current
tSW > Clock setting
iL
IOUT
Iripple
ILVLY
t
0
In valley control mode, minimum inductor current is regulated, not peak inductor current.
Figure 28. Valley Current Mode Operation
8.4.3.5 Dropout
Dropout operation is defined as any input-to-output voltage ratio that requires frequency to drop to achieve the
required duty cycle. At a given clock frequency, duty cycle is limited by minimum off-time. Once this limit is
reached, if clock frequency were maintained, output voltage would fall. Instead of allowing the output voltage to
drop, the LM61460-Q1 extends on-time past the end of the clock cycle until needed peak inductor current is
achieved. The clock is allowed to start a new cycle once peak inductor current is achieved or once a predetermined maximum on-time, tON_MAX, of approximately 9 µs passes. As a result, once the needed duty cycle
cannot be achieved at the selected clock frequency due to the existence of a minimum off-time, frequency drops
to maintain regulation. If input voltage is low enough so that output voltage cannot be regulated even with an ontime of tON_MAX, output voltage drops to slightly below input voltage, VDROP1. For additional information on
recovery from dropout, reference Figure 17.
Output Voltage
iL
VDROP1
Output
Setting
0
Switching Frequency
VDROP2 if
frequency =
1.85 MHz
Input
Voltage
Output
Voltage
Input Voltage
VIN
iL
Frequency
Setting
~100kHz
0
IOUT
Input Voltage
VIN
Output voltage and frequency versus input voltage: If there is little difference between input voltage and output
voltage setting, the IC reduces frequency to maintain regulation. If input voltage is too low to provide the desired
output voltage at approximately 110 kHz, input voltage tracks output voltage.
Figure 29. Frequency and Output Voltage in Dropout
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Device Functional Modes (continued)
SW Voltage
VSW
VIN
D=
tON
VOUT
§
tSW
VIN
tOFF = tOFF_MIN
tON < tON_MAX
0
- IOUTÂ5DSLS
t
Inductor Current
tSW > Clock setting
iL
ILPK
IOUT
0
Iripple
t
Switching waveforms while in dropout. Inductor current takes longer than a normal clock to reach the desired peak
value. As a result, frequency drops. This frequency drop is limited by tON_MAX.
Figure 30. Dropout Waveforms
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The LM61460-Q1 step-down DC-to-DC converter is typically used to convert a higher DC voltage to a lower DC
voltage with a maximum output current of 6 A. Using a 4-layer LM61460EVM, at 400 kHz the LM61460-Q1 can
sustain a continuous 6 A load up to an ambient temperature of approximately 95°C; see Figure 32. If ambient
temperature is 105°C and the frequency is set to 2.1 MHz, the current should be limited to 4 A; see Figure 33.
The following design procedure can be used to select components for the LM61460-Q1.
9.2 Typical Application
Figure 31 shows a typical application circuit for the LM61460-Q1. This device is designed to function with a wide
range of external components and system parameters. However, the internal compensation is optimized for a
certain range of external inductance and output capacitance. As a quick start guide, Table 3 provides typical
component values for some of the common configurations.
5 V to 36 V input
RENT
CIN_HF1
VIN1
VIN2
PGND1
CIN_HF2
CIN-BLK
PGND2
EN/SYNC
PGOOD
RPG
BIAS
Output
L1
SW
CBT
RT
COUT
RFF
CBOOT
RFBT
VCC
RRT
CFF
RBOOT
CVCC
AGND
FB
RFBB
Figure 31. Example Application Circuit
9.2.1 Design Requirements
Table 2 provides the parameters for our detailed design procedure example:
Table 2. Detailed Design Parameters
28
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage
13.5 V (5 V to 36 V)
Input voltage for constant fSW
8 V to 18 V
Output voltage
5V
Maximum output current
0 A to 6 A
Switching frequency
400 kHz
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Table 3. Typical External Component Values
fSW
(kHz)
VOUT (V)
L1 (µH)
COUT (RATED)
RFBT
(kΩ)
RFBB
(kΩ)
CBOOT
(µF)
RBOOT
(Ω)
CVCC
(µF)
CFF (pF)
RFF (kΩ)
2100
3.3
1
3 × 22 µF ceramic
100
43.2
0.1
0
1
10
1
400
3.3
4.7
3 × 47 µF ceramic
100
43.2
0.1
0
1
4.7
1
2100
5
1.5
2 × 22 µF ceramic
100
24.9
0.1
0
1
22
1
400
5
4.7
2 × 47 µF ceramic
100
24.9
0.1
0
1
22
1
9.2.2 Detailed Design Procedure
The following design procedure applies to Figure 31 and Table 2.
9.2.2.1 Choosing the Switching Frequency
The choice of switching frequency is a compromise between conversion efficiency and overall solution size.
Lower switching frequency implies reduced switching losses and usually results in higher system efficiency.
However, higher switching frequency allows for the use of smaller inductors and output capacitors, hence, a
more compact design.
When choosing operating frequency, the most important consideration is thermal limitations. This constraint
typically dominates frequency selection. See Figure 32 for circuits running at 400 kHz and Figure 33 for circuits
running at 2.1 MHz. These curves show how much output current can be supported at a given ambient
temperature given these switching frequencies. Note that power dissipation is layout dependent so while these
curves are a good starting point, thermal resistance in any design will be different from the estimates used to
generate Figure 32 and Figure 33. The maximum temperature ratings are based on the LM61460EVM, which is
approximately 100 mm x 80 mm in board area. Unless a larger copper area or cooling is provided to reduce the
effective RθJA, if ambient temperature is 105°C and the switching frequency is set to 2.1 MHz, the load current
should typically be limited to 4 A.
135
130
VIN = 13.5 V
VIN = 16 V
VIN = 24 V
120
VIN = 13.5 V
VIN = 16 V
VIN = 24 V
125
Ambient Temperature (°C)
Ambient Temperature (°C)
125
115
110
105
100
95
115
105
95
85
75
90
85
65
3
3.5
fSW = 400 kHz
4
4.5
5
Output Current (A)
PCB RθJA = 25°C/W
5.5
6
2
2.5
snvs
VOUT = 5 V
Figure 32. Maximum Ambient Temperature versus Output
Current
fSW = 2100 kHz
3
3.5
4
4.5
Output Current (A)
PCB RθJA =
25°C/W
5
5.5
6
snvs
VOUT = 5 V
Figure 33. Maximum Ambient Temperature versus Output
Current
Two other considerations are what maximum and minimum input voltage the part must maintain its frequency
setting. Since the LM61460-Q1 adjusts its frequency under conditions in which regulation would normally be
prevented by minimum on-time or minimum off time, these constraints are only important for input voltages
requiring constant frequency operation.
If foldback is undesirable at high input voltage, then use Equation 7:
fSW G
VOUT
VIN(MAX2) Â WON_MIN(MAX)
(7)
If foldback at low input voltage is a concern, use Equation 8:
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VINeff(MIN2) ± VOUT
VINeff(MIN2) Â WOFF_MIN(MAX)
fSW ”
where:
•
VINeff(MIN2) = VIN(MIN2) ± IOUT(MAX) Â (RDS(ON)_HS(MAX) + DCR(MAX))
•
•
•
DCR(MAX) = Maximum DCR of Inductor
tOFF_MIN(MAX) = See the Electrical Characteristics
RDS(ON)_HS(MAX) = See the Electrical Characteristics
(8)
The fourth constraint is the rated frequency range of the IC. See fADJ in the Electrical Characteristics. All four
constraints above, thermal, VIN(MAX2), VIN(MIN2), and device specified frequency range should be considered
when selecting frequency.
Many applications require that the AM band can be avoided. These applications tend to operate at either 400
kHz below the AM band or 2.1 MHz above the AM band. In this example, 400 kHz is chosen.
9.2.2.2 Setting the Output Voltage
The output voltage of LM61460-Q1 is externally adjustable using a resistor divider network. The range of
recommended output voltage is found in the Recommended Operating Conditions table. The divider network is
comprised of RFBT and RFBB, and closes the loop between the output voltage and the converter. The converter
regulates the output voltage by holding the voltage on the FB pin equal to the internal reference voltage, VREF.
The resistance of the divider is a compromise between excessive noise pick-up and excessive loading of the
output. Smaller values of resistance reduce noise sensitivity but also reduce the light-load efficiency. The
recommended value for RFBT is 100 kΩ with a maximum value of 1 MΩ. If 1 MΩ is selected for RFBT, then a
feedforward capacitor must be used across this resistor to provide adequate loop phase margin (see CFF and RFF
Selection). Once RFBT is selected, Equation 3 is used to select RFBB. VREF is nominally 1 V. For this 5-V example,
RFBT = 100 kΩ and RFBB = 24.9 kΩ are chosen.
9.2.2.3 Inductor Selection
The parameters for selecting the inductor are the inductance and saturation current. The inductance is based on
the desired peak-to-peak ripple current and is normally chosen to be in the range of 20% to 40% of the maximum
output current. Experience shows that the best value for inductor ripple current is 30% of the maximum load
current for systems with a fixed input voltage and 25% for systems with a variable input voltage such as the 12
volt battery in a car. Note that when selecting the ripple current for applications with much smaller maximum load
than the maximum available from the device, the maximum device current must still be used. Equation 9 can be
used to determine the value of inductance. The constant K is the percentage of inductor current ripple. For this
example, K = 0.25 was chosen and an inductance of approximately 5.25 μH was found. The next standard value
of 4.7 μH was selected.
L=
VIN Å 9OUT
VOUT
Â
fSW Â . Â ,OUT(MAX)
VIN
(9)
The saturation current rating of the inductor must be at least as large as the high-side switch current limit, IL-HS
(see the Electrical Characteristics section). This ensures that the inductor does not saturate even during a short
circuit on the output. When the inductor core material saturates, the inductance falls to a very low value, causing
the inductor current to rise very rapidly. Although the valley current limit, IL-LS, is designed to reduce the risk of
current run-away, a saturated inductor can cause the current to rise to high values very rapidly. This can lead to
component damage; do not allow the inductor to saturate. Inductors with a ferrite core material have very hard
saturation characteristics, but usually have lower core losses than powdered iron cores. Powdered iron cores
exhibit a soft saturation, allowing some relaxation in the current rating of the inductor. However, they have more
core losses at frequencies typically above 1 MHz. In any case, the inductor saturation current must not be less
than the device high-side current limit, IL-HS (see the Electrical Characteristics section). To avoid subharmonic
oscillation, the inductance value must not be less than that given in Equation 10. The maximum inductance is
limited by the minimum current ripple required for the current mode control to perform correctly. As a rule-ofthumb, the minimum inductor ripple current must be no less than about 10% of the device maximum rated
current under nominal conditions.
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/ • 0.32 Â
VOUT
fSW
(10)
Equation 10 assumes that this design must operate with input voltage near or in dropout. If minimum operating
voltage for this design is high enough to limit duty factor to below 50%, Equation 11 can be used in place of
Equation 10.
/ • 0.2 Â
VOUT
fSW
(11)
Note that choosing an inductor that is larger than the minimum inductance calculated using Equation 9 through
Equation 11 results in less output capacitance being needed to limit output ripple but more output capacitance
being needed to manage large load transients. See the Output Capacitor Selection section.
9.2.2.4 Output Capacitor Selection
The value of the output capacitor and its ESR determine the output voltage ripple and load
performance. The output capacitor is usually determined by the load transient requirements rather
output voltage ripple. Table 4 can be used to find the output capacitor and CFF selection for a few
applications. Note that a 1-kΩ RFF must be used in series with CFF. In this example, improved
performance is desired giving 2 x 47 µF ceramic as the output capacitor and 22 pF as CFF.
transient
than the
common
transient
Table 4. Recommended Output Ceramic Capacitors and CFF Values
3.3 V OUTPUT
5 V OUTPUT
TRANSIENT
PERFORMANCE
CERAMIC OUTPUT CAPACITANCE
CFF
CERAMIC OUTPUT CAPACITANCE
CFF
2.1 MHz
Minimum
3 x 22 µF
10 pF
2 x 22 µF
22 pF
2.1 MHz
Better Transient
2 x 47 µF
33 pF
3 x 22 µF
33 pF
400 kHz
Minimum
3 x 47 µF
4.7 pF
2 x 47 µF
10 pF
400 kHz
Better Transient
4 x 47 µF
33 pF
3 x 47 µF
33 pF
FREQUENCY
To minimize ceramic capacitance, a low-ESR electrolytic capacitor can be used in parallel with minimal ceramic
capacitance. As a starting point for designing with an output electrolytic capacitor, Table 5 shows the
recommended output ceramic capacitance CFF values when using an electrolytic capacitor.
Table 5. Recommended Electrolytic and ceramic Capacitor and CFF Values
FREQUENCY
400 kHz
400 kHz
3.3 V OUTPUT
TRANSIENT
PERFORMANCE
Minimum
Better Transient
COUT
2 x 47 µF ceramic + 1 x 470 µF, 100 mΩ electrolytic
3 x 47 µF ceramic + 2 x 280 µF,100 mΩ electrolytic
5 V OUTPUT
CFF
COUT
CFF
10 pF
3 x 22 µF ceramic + 1 x 470 µF, 100 mΩ
electrolytic
10 pF
33 pF
4 x 22 µF Ceramic + 1 x 560 µF, 100 mΩ
electrolytic
22 pF
Most ceramic capacitors deliver far less capacitance than the capacitor’s rating indicates. Be sure to check any
capacitor selected for initial accuracy, temperature derating and voltage derating. Table 4 and Table 5 have been
generated assuming typical derating for 16 V, X7R, automotive grade capacitors. If lower voltage, nonautomotive grade, or lower temperature rated capacitors are used, more capacitors than listed will likely be
needed.
9.2.2.5 Input Capacitor Selection
The ceramic input capacitors provide a low impedance source to the converter in addition to supplying the ripple
current and isolating switching noise from other circuits. A minimum of 10 μF of ceramic capacitance is required
on the input of the device. This must be rated for at least the maximum input voltage that the application
requires; preferably twice the maximum input voltage. This capacitance can be increased to help reduce input
voltage ripple and maintain the input voltage during load transients. In addition, a small case size 100-nF ceramic
capacitor must be used at each input/ground pin pair, VIN1/PGND1 and VIN2/PGND2, immediately adjacent to
the converter. This provides a high-frequency bypass for the control circuits internal to the device. These
capacitors also suppress SW node ringing, which reduces the maximum voltage present on the SW node and
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EMI. The two 100 nF must also be rated at 50 V with an X7R or better dielectric. The VQFN-HR (RJR) package
provides two input voltage pins and two power ground pins on opposite sides of the package. This allows the
input capacitors to be split, and placed optimally with respect to the internal power MOSFETs, thus improving the
effectiveness of the input bypassing. In this example, two 4.7-μF and two 100-nF ceramic capacitors are used,
one at each VIN/PGND location. A single 10-μF can also be used on one side of the package.
Many times, it is desirable and necessary to use an electrolytic capacitor on the input in parallel with the
ceramics. This is especially true if long leads or traces are used to connect the input supply to the converter. The
moderate ESR of this capacitor can help damp any ringing on the input supply caused by the long power leads.
The use of this additional capacitor also helps with momentary voltage dips caused by input supplies with
unusually high impedance.
Most of the input switching current passes through the ceramic input capacitors. The approximate worst case
RMS value of this current can be calculated from Equation 12 and must be checked against the manufacturers'
maximum ratings.
IRMS §
IOUT
2
(12)
9.2.2.6 BOOT Capacitor
The LM61460-Q1 requires a bootstrap capacitor connected between the CBOOT pin and the SW pin. This
capacitor stores energy that is used to supply the gate drivers for the high side power MOSFET. A high-quality
(X7R) ceramic capacitor of 100 nF and at least 10 V is required.
9.2.2.7 BOOT Resistor
A BOOT resistor can be connected between the CBOOT and RBOOT pins. Unless EMI for the application being
designed is critical, these two pins can be shorted. A 100 Ω resistor between these pins eliminates overshoot.
Even with 0 Ω, overshoot and ringing are minimal, less than 2 V if input capacitors are placed correctly. A boot
resistor of 100 Ω, which corresponds to approximately 2.7 ns SW node rise time and decreases efficiency by
approximately 0.5% at 2 MHz. To maximize efficiency, 0 Ω is chosen for this example. Under most
circumstances, selecting an RBOOT resistor value above 100 Ω is undesirable since the resulting small
improvement in EMI is not enough to justify further decreased efficiency.
9.2.2.8 VCC
The VCC pin is the output of the internal LDO used to supply the control circuits of the converter. This output
requires a 1-μF, 16-V ceramic capacitor connected from VCC to AGND for proper operation. In general, avoid
loading this output with any external circuitry. However, this output can be used to supply the pullup for the
power-good function (see the PGOOD Output Operation section). A pullup resistor with a value of 100 kΩ is a
good choice in this case. Note, VCC will remain high when VEN_WAKE< EN < VEN. The nominal output voltage on
VCC is 3.3 V. Do not short this output to ground or any other external voltage.
9.2.2.9 BIAS
Because VOUT = 5 V in this design, the BIAS pin is tied to VOUT to reduce LDO power loss. The output voltage is
supplying the LDO current instead of the input voltage. The power saving is ILDO × (VIN – VOUT). The power
saving is more significant when VIN >> VOUT and with higher frequency operation. To prevent VOUT noise and
transients from coupling to BIAS, a series resistor, 1 Ω to 10 Ω, can be added between VOUT and BIAS. A bypass
capacitor with a value of 1 μF or higher can be added close to the BIAS pin to filter noise. Note, the maximum
allowed voltage on the BIAS pin is 16 V.
9.2.2.10 CFF and RFF Selection
A feedforward capacitor, Cff, is used to improve phase margin and transient response of circuits which have
output capacitors with low ESR. Since this capacitor can conduct noise from the output of the circuit directly to
the FB node of the IC, a 1-kΩ resistor, Rff, must be placed in series with Cff. If the ESR zero of the output
capacitor is below 200 kHz, no Cff should be used.
If output voltage is less than 2.5 V, Cff has little effect so can be omitted. If output voltage is greater than 14 V, Cff
must not be used since it will introduce too much gain at higher frequencies.
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9.2.2.11 External UVLO
In some cases, an input UVLO level different than that provided internal to the device is needed. This can be
accomplished by using the circuit shown in Figure 34. The input voltage at which the device turns on is
designated VON while the turnoff voltage is VOFF. First, a value for RENB is chosen in the range of 10 kΩ to 100
kΩ, then Equation 14 is used to calculate RENT and VOFF. RENB is typically set based on how much current this
voltage divider should consume. RENB can be calculated using Equation 13.
RENB =
VEN Â 9IN
IDIVIDER Â 9ON
(13)
VIN
RENT
EN/SYNC
RENB
AGND
Figure 34. UVLO Using EN
RENT =
VON
Å 1 Â 5ENB
VEN
VOFF = VON Â (1 Å 9EN-HYST)
where
•
•
•
VON = VIN turnon voltage
VOFF = VIN turnoff voltage
IDIVIDER = voltage divider current
(14)
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9.2.3 Application Curves
Unless otherwise specified, the following conditions apply: VIN = 13.5 V, TA = 25°C. The circuit is shown in
Figure 31, with the appropriate BOM from Table 6.
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
60%
0.001
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
0.010.02 0.05 0.1 0.2 0.5
Output Current (A)
VOUT = 3.3 V
1
2 3 4 5 7 10
0
1
2
LM61
FSW = 400 kHz
Auto Mode
VOUT = 3.3 V
Figure 35. LM61460-Q1 Efficiency
3
4
Output Current (A)
5
6
7
LM61
FSW = 400 kHz
FPWM Mode
Figure 36. LM61460-Q1 Efficiency
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
60%
0.001
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
0.010.02 0.05 0.1 0.2 0.5
Output Current (A)
VOUT = 3.3 V
1
2 3 4 5 7 10
0
1
2
LM61
FSW = 2100 kHz
AUTO Mode
VOUT = 3.3 V
Figure 37. LM61460-Q1 Efficiency
3
4
Output Current (A)
5
6
7
LM61
FSW = 2100 kHz
FPWM Mode
Figure 38. LM61460-Q1 Efficiency
100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
60%
0.0001
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
0.001
VOUT = 5 V
0.01
0.1 0.2 0.5 1
Load Current (A)
FSW = 400 kHz
2 3 5 710
0
AUTO Mode
VOUT = 5 V
Figure 39. LM61460-Q1 Efficiency
34
1
LM61
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2
3
4
Load Current (A)
FSW = 400 kHz
5
6
7
LM61
FPWM Mode
Figure 40. LM61460-Q1 Efficiency
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100%
100%
95%
95%
90%
85%
Efficiency (%)
Efficiency (%)
90%
85%
80%
75%
80%
75%
70%
65%
70%
60%
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
65%
60%
0.001
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
55%
50%
0.010.02 0.05 0.1 0.2 0.5
Load Current (A)
VOUT = 5 V
FSW = 2100 kHz
1
2 3 4 5 7 10
0
1
2
LM61
AUTO Mode
VOUT = 5 V
Figure 41. LM61460-Q1 Efficiency
3
4
Load Current (A)
5
FSW = 2100 kHz
FPWM Mode
3.37
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
3.35
3.35
Output Voltage (V)
Output Voltage (V)
7
LM61
Figure 42. LM61460-Q1 Efficiency
3.37
3.33
3.31
3.33
3.31
3.29
3.29
0
1
2
VOUT = 3.3 V
3
4
Output Current (A)
5
6
7
0
1
2
SNVS
FSW = 400 kHz
Auto Mode
VOUT = 3.3 V
Figure 43. LM61460-Q1 Load and Line Regulation
3
4
Output Current (A)
5
6
7
SNVS
FSW = 400 kHz
FPWM Mode
Figure 44. LM61460-Q1 Load and Line Regulation
3.37
3.37
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
3.35
3.35
Output Voltage (V)
Output Voltage (V)
6
3.33
3.31
3.33
3.31
3.29
3.29
0
1
VOUT = 3.3 V
2
3
4
Output Current (A)
FSW = 2100 kHz
5
6
7
0
1
SNVS
AUTO Mode
Figure 45. LM61460-Q1 Load and Line Regulation
VOUT = 3.3 V
2
3
4
Output Current (A)
FSW = 2100 kHz
5
6
7
SNVS
FPWM Mode
Figure 46. LM61460-Q1 Load and Line Regulation
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5.11
5.11
5.09
5.09
5.07
5.07
Output Voltage (V)
Output Voltage (V)
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5.05
5.03
5.01
4.99
5.05
5.03
5.01
4.99
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
4.95
4.95
0
1
2
VOUT = 5 V
3
4
Output Current (A)
5
6
7
0
FSW = 400 kHz
AUTO Mode
2
VOUT = 5 V
5.11
5.11
5.09
5.09
5.07
5.07
5.05
5.03
5.01
3
4
Output Current (A)
4.99
6
7
SNVS
FSW = 400 kHz
FPWM Mode
5.05
5.03
5.01
4.99
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
4.95
4.95
0
1
2
VOUT = 5 V
3
4
Output Current (A)
5
6
7
0
1
2
SNVS
FSW = 2100 kHz
AUTO Mode
VOUT = 5 V
Figure 49. LM61460-Q1 Load and Line Regulation
3.25
3.25
Output Voltage (V)
3.5
3
3
4
Output Current (A)
5
6
7
SNVS
FSW = 2100 kHz
FPWM Mode
Figure 50. LM61460-Q1 Load and Line Regulation
3.5
2.75
3
2.75
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
2.5
2.5
3
3.25
VOUT = 3.3 V
3.5
3.75
4
4.25
Input Voltage (V)
FSW = 400 kHz
4.5
4.75
5
3
3.25
SNVS
AUTO Mode
VOUT = 3.3 V
Figure 51. LM61460-Q1 Dropout Curve
36
5
Figure 48. LM61460-Q1 Load and Line Regulation
Output Voltage (V)
Output Voltage (V)
1
SNVS
Figure 47. LM61460-Q1 Load and Line Regulation
Output Voltage (V)
VIN = 8 V
VIN = 13.5 V
VIN = 24 V
4.97
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3.5
3.75
4
4.25
Input Voltage (V)
FSW = 2100 kHz
4.5
4.75
5
SNVS
AUTO Mode
Figure 52. LM61460-Q1 Dropout Curve
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6
6
5.5
5.5
Ouput Voltage (V)
Output Voltage (V)
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5
4.5
4
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
3.5
5
4.5
4
IOUT = 0.01 A
IOUT = 3 A
IOUT = 6 A
3.5
3
3
4
4.2
4.4
4.6
VOUT = 5 V
4.8
5
5.2 5.4
Input Voltage (V)
5.6
5.8
6
4
4.2
FSW = 400 kHz
AUTO Mode
5E+5
2.5E+6
4.5E+5
2.25E+6
4E+5
2E+6
3.5E+5
3E+5
2.5E+5
2E+5
1.5E+5
1E+5
IOUT = 3 A
IOUT = 6 A
5E+4
4.8
5
5.2 5.4
Input Voltage (V)
5.6
5.8
6
SNVS
FSW = 2100 kHz
AUTO Mode
Figure 54. LM61460-Q1 Dropout Curve
Switching Frequency (Hz)
Switching Frequency (Hz)
4.6
VOUT = 5 V
Figure 53. LM61460-Q1 Dropout Curve
1.75E+6
1.5E+6
1.25E+6
1E+6
7.5E+5
5E+5
IOUT = 3 A
IOUT = 6 A
2.5E+5
0
0
3
3.25
3.5
VOUT = 3.3 V
3.75
4
Input Voltage (V)
4.25
3
4.5
3.5
snvs
FSW = 400 kHz
AUTO Mode
VOUT = 3.3 V
Figure 55. LM61460-Q1 Frequency Dropout
5E+5
2.5E+6
4.5E+5
2.25E+6
4E+5
2E+6
3.5E+5
3E+5
2.5E+5
2E+5
1.5E+5
1E+5
IOUT = 3 A
IOUT = 6 A
5E+4
4
Input Voltage (V)
4.5
5
snvs
FSW = 2100 kHz
AUTO Mode
Figure 56. LM61460-Q1 Frequency Dropout Curve
Switching Frequency (Hz)
Switching Frequency (Hz)
4.4
SNVS
1.75E+6
1.5E+6
1.25E+6
1E+6
7.5E+5
5E+5
IOUT = 3 A
IOUT = 6 A
2.5E+5
0
0
5
VOUT = 5 V
5.25
5.5
Input Voltage (V)
FSW = 400 kHz
5.75
6
5
snvs
AUTO Mode
Figure 57. LM61460-Q1 Frequency Dropout Curve
VOUT = 5 V
5.5
6
Input Voltage (V)
FSW = 2100 kHz
6.5
7
snvs
AUTO Mode
Figure 58. LM61460-Q1 Frequency Dropout Curve
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VOUT Ripple
(10 mV/DIV)
VOUT Ripple
(10 mV/DIV)
VSW
(5 V/DIV)
VSW
(5 V/DIV)
IINDUCTOR
(2 A/DIV)
IINDUCTOR
(2 A/DIV)
Time (20 µs/DIV)
VOUT = 5 V
IOUT = 50 mA
FSW = 2100 kHz
VIN = 13.5 V
Time (2 µs/DIV)
AUTO Mode
Figure 59. LM61460-Q1 Switching Waveform and VOUT
Ripple
VOUT = 5 V
IOUT = 50 mA
VOUT
(2 V/DIV)
IINDUCTOR
(1 A/DIV)
IINDUCTOR
(1 A/DIV)
VPG
(5 V/DIV)
VPG
(5 V/DIV)
VEN
(5 V/DIV)
VEN
(5 V/DIV)
Time (1 ms/DIV)
FSW = 2100 kHz
VIN = 13.5 V
FPWM Mode
Figure 60. LM61460-Q1 Switching Waveform and VOUT
Ripple
VOUT
(2 V/DIV)
VOUT = 5 V
IOUT = 50 mA
FSW = 2100 kHz
VIN = 13.5 V
Time (1 ms/DIV)
AUTO Mode
VOUT = 5 V
IOUT = 50 mA
Figure 61. LM61460-Q1 Start Up with 50-mA Load
VOUT
(2 V/DIV)
FSW = 2100 kHz
VIN = 13.5 V
FPWM Mode
Figure 62. LM61460-Q1 Start Up with 50-mA
VOUT
(2 V/DIV)
IINDUCTOR
(1 A/DIV)
VPG
(5 V/DIV)
IINDUCTOR
(2 A/DIV)
VEN
(5 V/DIV)
Time (1 ms/DIV)
VOUT = 3.3 V
IOUT = 3.25 A
FSW = 2100 kHz
VIN = 13.5 V
Time (200 µs/DIV)
FPWM Mode
VOUT = 5 V
IOUT = 5 A to Short
Circuit
FSW = 2100 kHz
VIN = 13.5 V
FPWM Mode
Figure 63. LM61460-Q1 Start Up with 3.25-A
Figure 64. LM61460-Q1 Short Circuit Protection
38
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VOUT
(2 V/DIV)
VOUT
(500 mV/DIV)
IINDUCTOR
(2 A/DIV)
IINDUCTOR
(2 A/DIV)
Time (20 ms/DIV)
VOUT = 5 V
IOUT = Short Circuit
to 5 A
FSW = 2100 kHz
VIN = 13.5 V
Time (20 ms/DIV)
FPWM Mode
VOUT = 5 V
IOUT = Short Circuit
FSW = 2100 kHz
VIN = 13.5 V
FPWM Mode
Figure 66. LM61460-Q1 Short Circuit Performance
Figure 65. LM61460-Q1 Short Circuit Recovery
VOUT
(2 V/DIV)
VOUT
(200 mV/DIV)
IINDUCTOR
(1 A/DIV)
VIN
(5 V/DIV)
IOUT
(2 A/DIV)
Time (2 ms/DIV)
VOUT = 5 V
IOUT = 4 A
FSW = 2100 kHz
VIN = 13.5 V to 4 V
to 13.5 V
Time (50 µs/DIV)
FPWM Mode
VOUT = 5 V
IOUT = 0 A to 6 A to
0A
Figure 67. Graceful Recovery from Dropout
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
FSW = 400 kHz
VIN = 13.5 V
AUTO Mode
TR = TF = 6 µs
Figure 68. LM61460-Q1 Load Transient
VOUT
(200 mV/DIV)
VOUT = 5 V
IOUT = 0 A to 6 A to
0A
FSW = 400 kHz
VIN = 13.5 V
Time (50 µs/DIV)
FPWM Mode
TR = TF = 6 µs
VOUT = 5 V
IOUT = 2 A to 5 A to
2A
Figure 69. LM61460-Q1 Load Transient
FSW = 400 kHz
VIN = 13.5 V
AUTO Mode
TR = TF = 3 µs
Figure 70. LM61460-Q1 Load Transient
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VOUT
(200 mV/DIV)
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
VOUT = 5 V
IOUT = 50 mA to 6
A to 50 mA
FSW = 400 kHz
VIN = 13.5 V
Time (50 µs/DIV)
AUTO Mode
TR = TF = 6 µs
VOUT = 3.3 V
IOUT = 0 A to 6 A to
0A
Figure 71. LM61460-Q1 Load Transient
VOUT
(200 mV/DIV)
FSW = 400 kHz
VIN = 13.5 V
AUTO Mode
TR = TF = 6 µs
Figure 72. LM61460-Q1 Load Transient
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
VOUT = 3.3 V
IOUT = 2 A to 4 A to
2A
FSW = 400 kHz
VIN = 13.5 V
Time (50 µs/DIV)
AUTO Mode
TR = TF = 2 µs
VOUT = 5 V
IOUT = 0 A to 6 A to
0A
Figure 73. LM61460-Q1 Load Transient
FSW = 2100 kHz
VIN = 13.5 V
AUTO Mode
TR = TF = 6 µs
Figure 74. LM61460-Q1 Load Transient
VOUT
(200 mV/DIV)
IOUT
(2 A/DIV)
Time (50 µs/DIV)
VOUT = 5 V
IOUT = 0 A to 6 A to
0A
FSW = 2100 kHz
VIN = 13.5 V
FPWM Mode
TR = TF = 6 µs
Figure 75. LM61460-Q1 Load Transient
40
FSW = 400 kHz
VOUT = 5 V
IOUT = 5 A
Frequency Tested: 150 kHz to 30 MHz
Figure 76. Conducted EMI versus CISPR25 Limits (Yellow:
Peak Signal, Blue: Average Signal)
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VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 30 MHz to 108 MHz
Figure 77. Conducted EMI versus CISPR25 Limits (Yellow:
Peak Signal, Blue: Average Signal)
VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 30 MHz to 300 MHz
Figure 79. Radiated EMI Bicon Vertical versus CISPR25
Limits
VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 300 MHz to 1 GHz
Figure 81. Radiated EMI Log Vertical versus CISPR25
Limits
VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 150 kHz to 30 MHz
Figure 78. Radiated EMI Rod versus CISPR25 Limits
VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 30 MHz to 300 MHz
Figure 80. Radiated EMI Bicon Horizontal versus CISPR25
Limits
VOUT = 5 V
FSW = 400 kHz
IOUT = 5 A
Frequency Tested: 300 MHz to 1 GHz
Figure 82. Radiated EMI Log Horizontal versus CISPR25
Limits
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744316220
L=2.2µH
VIN
IN+
IN-
GND
CF5=2.2uF
CF6=2.2uF
FSW = 400 kHz
CF3=2.2uF
CF4= 2.2uF
CF1=470nF
CF2=470nF
Note: Measurements taken with
LM61460EVM
Figure 83. Recommended Input EMI Filter
FSW = 2100 kHz
VOUT = 5 V
IOUT = 5 A
Frequency Tested: 150 kHz to 30 MHz
Figure 84. Conducted EMI versus CISPR25 Limits (Yellow:
Peak Signal, Blue: Average Signal)
74438356010
L=1µH
VIN
IN+
IN-
GND
CF5=2.2uF
CF6=2.2uF
FSW = 2100 kHz
VOUT = 5 V
IOUT = 5 A
Frequency Tested: 30 MHz to 108 MHz
CF3=2.2uF
CF4= 2.2uF
CF1=470nF
CF2=470nF
FSW = 2100 kHz
Figure 86. Recommended Input EMI Filter
Figure 85. Conducted EMI versus CISPR25 Limits (Yellow:
Peak Signal, Blue: Average Signal)
Table 6. BOM for Typical Application Curves
42
VOUT
FREQUENCY
RFBB
RT
COUT
CIN + CHF
L
3.3 V
400 kHz
43.2 kΩ
33.2 kΩ
6 x 22 µF
2 x 4.7 µF + 2 x 100 nF
4.7 µH (XHMI6060)
3.3 V
2100 kHz
43.2 kΩ
6.04 kΩ
3 x 22 µF
2 x 4.7 µF + 2 x 100 nF
1 µH (XEL5030)
5V
400 kHz
24.9 kΩ
33.2 kΩ
4 x 22 µF
2 x 4.7 µF + 2 x 100 nF
4.7 µH (XHMI6060)
5V
2100 kHz
24.9 kΩ
6.04 kΩ
3 x 22 µF
2 x 4.7 µF + 2 x 100 nF
1 µH (XEL5030)
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10 Power Supply Recommendations
The characteristics of the input supply must be compatible with the Absolute Maximum Ratings and
Recommended Operating Conditions in this data sheet. In addition, the input supply must be capable of
delivering the required input current to the loaded converter. The average input current can be estimated with
Equation 15.
IIN =
VOUT Â ,OUT
VIN Â
where
•
η is the efficiency
(15)
If the converter is connected to the input supply through long wires or PCB traces, special care is required to
achieve good performance. The parasitic inductance and resistance of the input cables can have an adverse
effect on the operation of the converter. The parasitic inductance, in combination with the low-ESR, ceramic input
capacitors, can form an under-damped resonant circuit, resulting in overvoltage transients at the input to the
converter or tripping UVLO. The parasitic resistance can cause the voltage at the VIN pin to dip whenever a load
transient is applied to the output. If the application is operating close to the minimum input voltage, this dip can
cause the converter to momentarily shutdown and reset. The best way to solve these kind of issues is to reduce
the distance from the input supply to the converter and use an aluminum input capacitor in parallel with the
ceramics. The moderate ESR of this type of capacitor helps damp the input resonant circuit and reduce any
overshoot or undershoot at the input. A value in the range of 20 µF to 100 µF is usually sufficient to provide input
damping and help hold the input voltage steady during large load transients.
In some cases, a transient voltage suppressor (TVS) is used on the input of converters. One class of this device
has a snap-back characteristic (thyristor type). The use of a device with this type of characteristic is not
recommended. When the TVS fires, the clamping voltage falls to a very low value. If this voltage is less than the
output voltage of the converter, the output capacitors discharge through the device back to the input. This
uncontrolled current flow can damage the TVS and cause large input transients.
The input voltage must not be allowed to fall below the output voltage. In this scenario, such as a shorted input
test, the output capacitors discharge through the internal parasitic diode found between the VIN and SW pins of
the device. During this condition, the current can become uncontrolled, possibly causing damage to the device. If
this scenario is considered likely, then a Schottky diode between the input supply and the output must be used.
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11 Layout
11.1 Layout Guidelines
The PCB layout of any DC-DC converter is critical to the optimal performance of the design. Bad PCB layout can
disrupt the operation of an otherwise good schematic design. Even if the converter regulates correctly, bad PCB
layout can mean the difference between a robust design and one that cannot be mass produced. Furthermore,
the EMI performance of the converter is dependent on the PCB layout, to a great extent. In a buck converter, the
most critical PCB feature is the loop formed by the input capacitor or capacitors and power ground, as shown in
Figure 87. This loop carries large transient currents that can cause large transient voltages when reacting with
the trace inductance. These unwanted transient voltages disrupt the proper operation of the converter. Because
of this, the traces in this loop must be wide and short, and the loop area as small as possible to reduce the
parasitic inductance. Figure 88 shows a recommended layout for the critical components for the circuit of the
LM61460-Q1.
• Place the input capacitor or capacitors as close as possible input pin pairs: VIN1 to PGND1 and VIN2 to
PGND2. Each pair of pins are adjacent, simplifying the input capacitor placement. With the VQFN-HR
package, there are two VIN/PGND pairs on either side of the package. This provides for a symmetrical layout
and helps minimize switching noise and EMI generation. Use a wide VIN plane on a lower layer to connect
both of the VIN pairs together to the input supply.
• Place bypass capacitor for VCC close to the VCC pin and AGND pins: This capacitor must routed with short,
wide traces to the VCC and AGND pins.
• Use wide traces for the CBOOT capacitor: Place the CBOOT capacitor as close to the device with short, wide
traces to the CBOOT and SW pins. It is important to route the SW connection under the device through the
gap between VIN2 and RBOOT pins, reducing exposed SW node area. If an RBOOT resistor is used, place
as close as possible to CBOOT and RBOOT pins. If high efficiency is desired, RBOOT and CBOOT pins can
be shorted. This short must be placed as close as possible to RBOOT and CBOOT pins as possible.
• Place the feedback divider as close as possible to the FB pin of the device: Place RFBB, RFBT, and CFF, if
used, physically close to the device. The connections to FB and AGND through RFBB must be short and close
to those pins on the device. The connection to VOUT can be somewhat longer. However, this latter trace must
not be routed near any noise source (such as the SW node) that can capacitively couple into the feedback
path of the converter.
• Layer 2 of the PCB must be a ground plane: This plane acts as a noise shield and a heat dissipation path.
Using layer 2 reduces the inclosed area in the input circulating current in the input loop, reducing inductance.
• Provide wide paths for VIN, VOUT, and GND: These paths must be wide and direct as possible to reduce any
voltage drops on the input or output paths of the converter and maximizes efficiency.
• Provide enough PCB area for proper heat sinking: Enough copper area must be used to ensure a low RθJA,
commensurate with the maximum load current and ambient temperature. Make the top and bottom PCB
layers with two-ounce copper and no less than one ounce. If the PCB design uses multiple copper layers
(recommended), thermal vias can also be connected to the inner layer heat-spreading ground planes. Note
that the package of this device dissipates heat through all pins. Wide traces must be used for all pins except
where noise considerations dictate minimization of area.
• Keep switch area small: Keep the copper area connecting the SW pin to the inductor as short and wide as
possible. At the same time, the total area of this node must be minimized to help reduce radiated EMI.
44
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Layout Guidelines (continued)
VIN1
VIN2
HS
FET
CIN_HF1
CIN_HF2
SW
LS
FET
PGND1
PGND2
Figure 87. Input Current Loop
11.1.1 Ground and Thermal Considerations
As mentioned above, TI recommends using one of the middle layers as a solid ground plane. A ground plane
provides shielding for sensitive circuits and traces. It also provides a quiet reference potential for the control
circuitry. The AGND and PGND pins must be connected to the ground planes using vias next to the bypass
capacitors. PGND pins are connected directly to the source of the low-side MOSFET switch, and also connected
directly to the grounds of the input and output capacitors. The PGND net contains noise at the switching
frequency and can bounce due to load variations. The PGND trace, as well as the VIN and SW traces, must be
constrained to one side of the ground planes. The other side of the ground plane contains much less noise and
must be used for sensitive routes.
TI recommends providing adequate device heat sinking by using vias near ground and VIN to connect to the
system ground plane or VIN strap, both of which dissipate heat. Use as much copper as possible, for system
ground plane, on the top and bottom layers for the best heat dissipation. Use a four-layer board with the copper
thickness for the four layers, starting from the top as: 2 oz / 1 oz / 1 oz / 2 oz. A four-layer board with enough
copper thickness and proper layout, provides low current conduction impedance, proper shielding, and lower
thermal resistance.
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11.2 Layout Example
GND POUR
VIAS to BIAS
VIA to Feedback
divider
VOUT
COUT2
COUT1
GND POUR
GND POUR
INDUCTOR
Inductor
CIN_HF2
CIN2
CIN_HF1
11
10
12
9
CIN1
8
VIN
7
6
13
14
CBOOT
1
2 3 4
VIN
5
RBOOT
VOUT
LM61460-Q1
REN
CVCC
RT
RFBB
CFF
GND POUR
RFBT
RFF
GND POUR
VOUT
INNER GND PLANE ± LAYER 2
Top Trace/Pour
VIA to Signal Layer
Inner GDN Plane
VIA to GND
VIN Strap on Inner Layer
VIA to VIN Strap
Figure 88. Layout Example
46
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12 Device and Documentation Support
12.1 Documentation Support
12.1.1 Related Documentation
For related documentation see the following:
• Texas Instruments, Designing High Performance, Low-EMI, Automotive Power Supplies Application Report
• Texas Instruments, LM61460-Q1 EVM User's Guide
• Texas Instruments, 30 W Power for Automotive Dual USB Type-C Charge Port Reference Design
• Texas Instruments, EMI Filter Components and Their Nonidealities for Automotive DC/DC Regulators
Technical Brief
• Texas Instruments, AN-2020 Thermal Design by Insight, Not Hindsight Application Report
• Texas InstrumentsOptimizing the Layout for the TPS54424/TPS54824 HotRod QFN Package for Thermal
Performance Application Report
• Texas Instruments, AN-2162 Simple Success With Conducted EMI From DC-DC Converters Application
Report
• Texas Instruments, Practical Thermal Design With DC/DC Power Modules Application Report
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.3 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
12.4 Trademarks
Hotrod, E2E are trademarks of Texas Instruments.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OUTLINE
RJR0014A
VQFN-HR - 1 mm max height
SCALE 3.200
PLASTIC QUAD FLATPACK - NO LEAD
4.1
3.9
B
A
PIN 1 INDEX AREA
3.6
3.4
0.1 MIN
(0.05)
SECTION A-A
SECTION
A-A
SCALE
30.000
TYPICAL
1.0
0.8
C
SEATING PLANE
0.05
0.00
0.08 C
2X 0.625
2X 1.6
2X 0.5
2X 0.45
2X 0.55
0.1
0.05
0.4
0.3
C A B
C
0.35
0.25
2X
6
0.7
0.5
(0.2) TYP
9
5
A
2X 0.525
0.45
0.35
A
SYMM
10
2X 1.15
2.2 0.05
PIN 1
ID
2X
11
1
0.45
0.35
C A B
C
0.9
0.7
4X
0.1
0.05
2X
14
0.6
0.4
2X
0.3
0.2
C A B
C
PKG
6X
0.1
0.05
7X
0.6
0.4
0.45
2X
0.35
0.1
0.05
0.45
0.35
0.1
0.05
C A B
C
C A B
C
4223976/D 11/2019
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
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EXAMPLE BOARD LAYOUT
RJR0014A
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.7)
PKG
(0.5)
2X
(0.35)
(0.625)
4X (1)
14
2X (0.8)
2X
(0.4)
2X
(0.4)
2X (1)
1
11
4X (0.4)
SEE SOLDER MASK
DETAIL
(2.4)
(0.3)
SYMM
10
(0.4)
(0.525)
(3.2)
(1)
(R0.05)
TYP
(2.9)
7X (0.7)
9
5
6
6X (0.25)
(0.45)
(1.85)
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE: 25X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
METAL UNDER
SOLDER MASK
METAL EDGE
EXPOSED
METAL
SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
(PREFERRED)
EXPOSED
METAL
SOLDER MASK
OPENING
SOLDER MASK DEFINED
SOLDER MASK DETAIL
4223976/D 11/2019
NOTES: (continued)
3. This package is designed to be soldered to thermal pads on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
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EXAMPLE STENCIL DESIGN
RJR0014A
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.8)
(0.625)
2X
(0.3)
4X (1)
PKG
(0.5)
2X (0.7)
2X
(0.35)
2X
(0.4)
14
EXPOSED METAL
TYP
2X (1)
1
11
4X (0.35)
2X (1.1)
(2.9)
(0.3)
SYMM
10
2X (0.4)
(0.525)
(3.2)
(0.35)
EXPOSED
METAL
(1.65)
(R0.05)
TYP
7X (0.7)
9
5
6
6X (0.25)
(0.45)
(1.85)
SOLDER PASTE EXAMPLE
BASED ON 0.1 mm THICK STENCIL
PADS 1, 5, 9 & 11:
90% PRINTED SOLDER COVERAGE BY AREA
SCALE: 25X
4223976/D 11/2019
NOTES: (continued)
4. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
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PACKAGE OPTION ADDENDUM
www.ti.com
7-Jan-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
LM61460AASQRJRRQ1
ACTIVE
Package Type Package Pins Package
Drawing
Qty
VQFN-HR
RJR
14
3000
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
Op Temp (°C)
Device Marking
(4/5)
-40 to 150
6146Q1
AAS
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE MATERIALS INFORMATION
www.ti.com
21-Dec-2019
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
LM61460AASQRJRRQ1
Package Package Pins
Type Drawing
VQFNHR
RJR
14
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
3000
330.0
12.4
Pack Materials-Page 1
3.8
B0
(mm)
K0
(mm)
P1
(mm)
4.3
1.15
8.0
W
Pin1
(mm) Quadrant
12.0
Q2
PACKAGE MATERIALS INFORMATION
www.ti.com
21-Dec-2019
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM61460AASQRJRRQ1
VQFN-HR
RJR
14
3000
370.0
355.0
55.0
Pack Materials-Page 2
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