Texas Instruments | LMR34206-Q1 4.2-V to 42-V, 0.6-A Ultra-Small Synchronous Step-Down Converter (Rev. A) | Datasheet | Texas Instruments LMR34206-Q1 4.2-V to 42-V, 0.6-A Ultra-Small Synchronous Step-Down Converter (Rev. A) Datasheet

Texas Instruments LMR34206-Q1 4.2-V to 42-V, 0.6-A Ultra-Small Synchronous Step-Down Converter (Rev. A) Datasheet
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LMR34206-Q1
SNVSBA8A – MAY 2019 – REVISED OCTOBER 2019
LMR34206-Q1 4.2-V to 42-V, 0.6-A Ultra-Small Synchronous Step-Down Converter
1 Features
2 Applications
•
•
•
•
•
1
•
•
•
•
•
AEC-Q100-qualified for automotive applications:
– Temperature grade 1: –40°C to +125°C, TA
Designed for automotive applications
– Junction temperature range –40°C to +150°C
– Protection features: thermal shutdown, input
undervoltage lockout, cycle-by-cycle current
limit, hiccup short-circuit protection
– 0.2-V dropout with 0.6-A load (typical)
– ±1.5% reference voltage tolerance
– 3.3-V, 5-V fixed-output voltage options
Suited for scalable power supplies
– Pin compatible with:
– LMR36015/06-Q1 (60 V, 0.6 A or 1.5 A)
– LMR33620/30-Q1 (36 V, 2 A, or 3 A)
– 2.1-MHz frequency option
Integration reduces solution size and cost
– Small, 2-mm × 3-mm VQFN package with
wettable flanks
– Few external components
Low power dissipation across load spectrum
– Increased light load efficiency in PFM
– Low operating quiescent current of 24 µA
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
ADAS camera module
Head-up display
Body control module
General purpose wide VIN power supplies
3 Description
The LMR34206-Q1 regulator is an easy-to-use,
synchronous, step-down DC/DC converter. With
integrated high-side and low-side power MOSFETs,
up to of output current is delivered over a wide input
voltage range of 4.2 V to 42 V.
The LMR34206-Q1 uses peak-current-mode control
to provide optimal efficiency and output voltage
accuracy. Precision enable gives flexibility by
enabling a direct connection to the wide input voltage
or precise control over device start-up and shutdown.
The power-good flag, with built-in filtering and delay,
offers a true indication of system status eliminating
the requirement for an external supervisor.
The LMR34206-Q1 is in a HotRod™ package which
enables low EMI, higher efficiency, and the smallest
package to die ratio. The device requires few external
components and has a pinout designed for simple
PCB layout. The small solution size and feature set of
the LMR34206-Q1 are designed to simplify
implementation for a wide range of end equipment.
Device Information(1)
PART NUMBER
LMR34206-Q1
PACKAGE
BODY SIZE (NOM)
VQFN-HR (12)
2.00 mm × 3.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Figure 1. Simplified Schematic
BOOT
VIN
VIN
CIN
CBOOT
EN
VOUT
SW
L1
COUT
PGND
LMR34206-Q1
PG
VCC
CVCC
FB
AGND
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.
LMR34206-Q1
SNVSBA8A – MAY 2019 – REVISED OCTOBER 2019
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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
3
4
5
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
5
5
5
6
6
7
8
9
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions ......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
System Characteristics .............................................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
8.1 Overview ................................................................. 10
8.2 Functional Block Diagram ....................................... 11
8.3 Feature Description................................................. 11
8.4 Device Functional Modes........................................ 16
9
Application and Implementation ........................ 20
9.1 Application Information............................................ 20
9.2 Typical Application ................................................. 20
10 Power Supply Recommendations ..................... 29
11 Layout................................................................... 30
11.1 Layout Guidelines ................................................. 30
11.2 Layout Example .................................................... 32
12 Device and Documentation Support ................. 33
12.1
12.2
12.3
12.4
12.5
12.6
12.7
Device Support ....................................................
Documentation Support ........................................
Receiving Notification of Documentation Updates
Support Resources ...............................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
33
33
33
34
34
34
34
13 Mechanical, Packaging, and Orderable
Information ........................................................... 34
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (May 2019) to Revision A
Page
•
Added EMI description to the Features .................................................................................................................................. 1
•
Replaced Figure 36 with the correct graph .......................................................................................................................... 27
2
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5 Device Comparison Table
ORDERABLE PART
NUMBER
OUTPUT VOLTAGE
SPREAD
SPECTRUM
FPWM
fSW
PACKAGE QUANTITY
LMR34206FSC3RNXTQ1
3.3-V fixed
Yes
Yes
2.1 MHz
250
3000
LMR34206FSC3RNXRQ1
3.3-V fixed
Yes
Yes
2.1 MHz
LMR34206SC3QRNXTQ1
3.3-V fixed
Yes
No
2.1 MHz
250
LMR34206SC3QRNXRQ1
3.3-V fixed
Yes
No
2.1 MHz
3000
LMR34206FSC5RNXTQ1
5-V fixed
Yes
Yes
2.1 MHz
250
3000
LMR34206FSC5RNXRQ1
5-V fixed
Yes
Yes
2.1 MHz
LMR34206SC5QRNXTQ1
5-V fixed
Yes
No
2.1 MHz
250
LMR34206SC5QRNXRQ1
5-V fixed
Yes
No
2.1 MHz
3000
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6 Pin Configuration and Functions
RNX Package
12-Pin VQFN-HR
Top View
SW
12
5
PGND 1
11 PGND
10 VIN
VIN 2
NC
3
9 EN
BOOT
4
8 PG
5
6
7
VCC AGND FB
Pin Functions
NO.
NAME
TYPE
DESCRIPTION
1, 11
PGND
G
Power ground terminal. Connect to system ground and AGND. Connect to CIN with short wide traces.
2, 10
VIN
P
Input supply to regulator. Connect to CIN with short wide traces.
3
NC
—
Connect the SW pin to NC on the PCB. This simplifies the connection from the CBOOT capacitor to the
SW pin. This pin has no internal connection to the regulator.
4
BOOT
P
Boot-strap supply voltage for internal high-side driver. Connect a high-quality 100-nF capacitor from this
pin to the SW pin. Connect the SW pin to NC on the PCB. This simplifies the connection from the CBOOT
capacitor to the SW pin.
5
VCC
P
Internal 5-V LDO output. Used as supply to internal control circuits. Do not connect to external loads.
Can be used as logic supply for power-good flag. Connect a high-quality 1-µF capacitor from this pin to
GND.
6
AGND
G
Analog ground for regulator and system. Ground reference for internal references and logic. All electrical
parameters are measured with respect to this pin. Connect to system ground on PCB.
7
FB
A
Feedback input to regulator. Connect to tap point of feedback voltage divider. DO NOT FLOAT. DO
NOT GROUND.
8
PG
A
Open drain power-good flag output. Connect to suitable voltage supply through a current limiting
resistor. High = power OK, low = power bad. Goes low when EN = Low. Can be open or grounded when
not used.
9
EN
A
Enable input to regulator. High = ON, low = OFF. Can be connected directly to VIN; DO NOT FLOAT.
12
SW
P
Regulator switch node. Connect to power inductor. Connect the SW pin to NC on the PCB. This
simplifies the connection from the CBOOT capacitor to the SW pin.
A = Analog, P = Power, G = Ground
4
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7 Specifications
7.1 Absolute Maximum Ratings
Over operating junction temperature range of -40°C to 150°C (unless otherwise noted) (1)
MIN
MAX
VIN to PGND
–0.3
45
V
EN to AGND
–0.3
45.3
V
FB to AGND
–0.3
5.5
V
PG to AGND
–0.3
22
V
AGND to PGND
–0.3
0.3
V
SW to PGND
–0.3
45.3
V
SW to PGND less than 10-ns negative transient
–3.5
CBOOT to SW
–0.3
5.5
VCC to AGND
–0.3
5.5
V
Junction Temperature TJ
-40
150
°C
Storage temperature, Tstg
–65
150
°C
Input voltage
Output voltage
(1)
UNIT
V
V
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.
7.2 ESD Ratings
V(ESD)
Electrostatic
discharge
Human-body model (HBM), per AEC Q100-002 (1)
HBM ESD Classification Level 2
V(ESD)
Electrostatic
discharge
Charged-device model (CDM), per AEC Q100-011
CDM ESD Classification Level C5
(1)
VALUE
UNIT
±2500
V
±750
V
AEC Q100-002 indicates that HBM stressing shall be in accordance with ANSI/ESDA/JEDEC JS-001 specification
7.3 Recommended Operating Conditions
Over the recommended operating junction temperature range of –40 ℃ to 150 ℃ (unless otherwise noted) (1)
MIN
MAX
4.2
42
V
EN to PGND (2)
0
42
V
(2)
0
18
V
0
0.6
A
VIN to PGND
Input voltage
PG to PGND
Output current
(1)
(2)
IOUT
UNIT
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.
The voltage on this pin must not exceed the voltage on the VIN pin by more than 0.3 V.
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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 can not 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 design information see Maximum Ambient
Temperature section.
LMR34206-Q1
THERMAL METRIC (1) (2)
RNX (VQFN-HR)
UNIT
12 PINS
RθJA
Junction-to-ambient thermal resistance
72.5
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
35.9
°C/W
RθJB
Junction-to-board thermal resistance
23.3
°C/W
ψJT
Junction-to-top characterization parameter
0.8
°C/W
ψJB
Junction-to-board characterization parameter
23.5
°C/W
(1)
(2)
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 can not 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 design information see Maximum Ambient Temperature section.
7.5 Electrical Characteristics
Limits apply over operating junction temperature (TJ ) range of –40°C to +150°C, unless otherwise stated. Minimum and
Maximum limits (1) 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 = 12V.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
14
24
35
UNIT
SUPPLY VOLTAGE (VIN PIN)
IQ-nonSW
Operating quiescent current (nonswitching) (2)
VEN = 3.3 V (PFM variant only)
ISD
Shutdown quiescent current;
measured at VIN pin
VEN = 0 V
3.3
µA
µA
ENABLE (EN PIN)
VEN-VCC-H
Enable input high level for VCC output
VENABLE rising; Internal LDO turns ON
VEN-VCC-L
Enable input low level for VCC output
VENABLE falling; Internal LDO turns
OFF
1.14
VEN-VOUT-H
Enable input high level for VOUT
VENABLE rising; Switching ON
1.157
1.231
1.3
V
VEN-VOUT-HYS
Enable input hysteresis for VOUT
Hysteresis below VEN-VOUT-H;
Switching OFF
45
110
175
mV
ILKG-EN
Enable input leakage current
VEN = 3.3V
0.2
50
nA
4.75
5
5.25
V
0.3
V
V
INTERNAL LDO (VCC PIN)
VCC
VCC-UVLORising
VCC-UVLOFalling
Internal VCC voltage
6 V ≤ VIN ≤ 42 V
Internal VCC undervoltage lockout
VCC rising
3.6
3.8
4.0
V
Internal VCC undervoltage lockout
VCC falling
3.1
3.3
3.5
V
VOLTAGE REFERENCE (FB PIN)
V5v0-Fixed
5 V Fixed Output voltage
Fixed output voltage option
4.9
5
5.1
V
V3v3-Fixed
3.3 V Fixed Output voltage
Fixed output voltage option
3.23
3.3
3.37
V
ILKG-5v0-Fixed
Feedback leakage current; 5v0 Fixed
VOUT = 5 V (Fixed output voltage
option only)
2.5
2.9
µA
ILKG-3v3V-Fixed
Feedback leakage current; 3v3 Fixed
VOUT = 3.3 V (Fixed output voltage
option only)
1.4
1.8
µA
(1)
(2)
6
MIN and MAX limits are 100% production tested at 25℃. Limits over the operating temperature range verified through correlation using
Statistical Quality Control (SQC) methods. Limits are used to calculate Average Outgoing Quality Level (AOQL).
This is the current used by the device open loop. It does not represent the total input current of the system when in regulation.
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Electrical Characteristics (continued)
Limits apply over operating junction temperature (TJ ) range of –40°C to +150°C, unless otherwise stated. Minimum and
Maximum limits(1) 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 = 12V.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
CURRENT LIMITS AND HICCUP
ISC
High-side current limit (3)
0.8
1
1.2
A
ILS-LIMIT
Low-side current limit (3)
0.6
0.8
0.95
A
IL-ZC
Zero cross detector threshold
IPEAK-MIN
Minimum inductor peak current (3)
IL-NEG
Negative current limit (3)
PFM variants only
0.02
A
0.18
A
FPWM variant only
-0.95
–0.6
–0.25
A
POWER GOOD (PGOOD PIN)
VPG-HIGH-UP
Power-Good upper threshold - rising
% of FB voltage
105%
107%
110%
VPG-LOW-DN
Power-Good lower threshold - falling
% of FB voltage
90%
93%
95%
VPG-HYS
Power-Good hysteresis (rising &
falling)
% of FB voltage
TPG
Power-Good rising/falling edge
deglitch delay
VPG-VALID
Minimum input voltage for proper
Power-Good function
RPG
Power-Good on-resistance
VEN = 2.5 V
RPG
Power-Good on-resistance
VEN = 0 V
Internal oscillator frequency
2.1-MHz variant
RDS-ON-HS
High-side MOSFET ON-resistance
RDS-ON-LS
Low-side MOSFET ON-resistance
2%
80
140
200
µs
2
V
80
165
Ω
35
90
Ω
2.1
2.35
MHz
IOUT = 0.5 A
225
435
mΩ
IOUT = 0.5 A
150
280
mΩ
OSCILLATOR
FOSC
1.95
MOSFETS
(3)
The current limit values in this table are tested, open loop, in production. They may differ from those found in a closed loop application.
7.6 Timing Requirements
Limits apply over operating junction temperature (TJ ) range of –40°C to +150°C, unless otherwise stated. Minimum and
Maximum limits (1) 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 = 12 V.
NOM
MAX
tON-MIN
Minimum switch on-time
MIN
55
83
tOFF-MIN
Minimum switch off-time
53
73
ns
tON-MAX
Maximum switch on-time
7
12
µs
tSS
Internal soft-start time
4.5
6
ms
(1)
3
UNIT
ns
MIN and MAX limits are 100% production tested at 25℃. Limits over the operating temperature range verified through correlation using
Statistical Quality Control (SQC) methods. Limits are used to calculate Average Outgoing Quality Level (AOQL).
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7.7 System Characteristics
The following specifications apply to a typical application circuit with nominal component values. Specifications in the typical
(TYP) column apply to TJ = 25℃ only. Specifications in the minimum (MIN) and maximum (MAX) columns apply to the case
of typical components over the temperature range of TJ = –40℃ to 150℃. These specifications are not ensured by production
testing.
PARAMETER
TEST CONDITIONS
MIN
TYP
UNIT
Operating input voltage range
VOUT
Voltage regulation for VOUT = 3.3 V
fixed (1)
FPWM operation
ISUPPLY
Input supply current when in regulation
VIN = 12 V, VOUT = 3.3 V Fixed, PFM variant
DMAX
Maximum switch duty cycle (2)
VHC
FB pin voltage required to trip short-circuit
hiccup mode
0.4
V
tHC
Time between current-limit hiccup burst
94
ms
tD
Switch voltage dead time
2
ns
FsSS
Frequency span of spread spectrum
operation
±4
%
FrSS
Triangular spread spectrum repetition
frequency
16
kHz
TSD
Thermal shutdown temperature
Shutdown temperature
170
°C
TSD
Thermal shutdown temperature
Recovery temperature
158
°C
(1)
(2)
8
4.2
MAX
VIN
3.28
3.33
26
42
V
3.37
V
µA
98%
Deviation in VOUT from nominal output voltage value at VIN = 24 V, IOUT = 0 A to 0.6A
In dropout the switching frequency drops to increase the effective duty cycle. The lowest frequency is clamped at approximately: FMIN =
1 / (tON-MAX + tOFF-MIN). DMAX = tON-MAX /(tON-MAX + tOFF-MIN).
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7.8 Typical Characteristics
Unless otherwise specified the following conditions apply: TA = 25°C. VIN = 24 V.
30
12
29
10
Shutdown Current (µA)
Quiescent Current (µA)
28
27
26
25
24
23
22
8
6
4
25C
150C
-40C
21
20
2
6
10
14
18
22
26
30
Input Voltage (V)
34
38
42
6
10
VFB = 1 V
22
26
30
Input Voltage (V)
34
38
42
Shut
Figure 3. Shutdown Supply Current
1.5
1
1.3
0.8
Current (A)
Current (A)
18
EN = 0 V
Figure 2. Non-Switching Input Supply Current
1.1
0.9
0.6
0.4
0.2
0.7
0.5
-40
0
40
80
Temperatuer (°C)
120
0
-40
150
hs-c
0
120
150
ls-c
Figure 5. Low Side Current Limit
Figure 4. High Side Current Limit
425
1.016
400
Peak Inductor Current (mA)
1.02
1.012
1.008
1.004
1
0.996
0.992
0.988
375
350
325
300
275
250
225
0.984
0.98
-40
40
80
Temperature (°C)
VIN = 24 V
VIN = 24 V
Voltage (V)
14
LMR3
200
0
40
80
Temperature (°C)
120
150
vref
5
10
IOUT = 0 A
ƒSW = 2100 kHz
Figure 6. Reference Voltage Drift
15
20
25
30
Input Voltage (V)
35
40
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VOUT = 3.3V
Figure 7. IPEAK-MIN
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8 Detailed Description
8.1 Overview
The LMR34206-Q1 is a synchronous peak-current-mode buck regulator designed for a wide variety of
applications. The regulator automatically switches modes between PFM and PWM depending on load. At heavy
loads, the device operates in PWM at a constant switching frequency. At light loads the mode changes to PFM,
with diode emulation allowing DCM. This reduces the input supply current and keeps efficiency high. The device
features internal loop compensation which reduces design time and requires fewer external components than
externally compensated regulators.
The LMR34206-Q1 is designed with a flip-chip or HotRod™ technology, greatly reducing the parasitic inductance
of pins. In addition, the layout of the device allows for reduction in the radiated noise generated by the switching
action through partial cancellation of the current generated magnetic field. As a result the switch-node waveform
exhibits less overshoot and ringing.
2V/div
50ns/div
BW:500MHz
Figure 8. Switch Node Waveform
10
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8.2 Functional Block Diagram
VCC
INT. REG.
BIAS
OSCILLATOR
EN
VIN
ENABLE
LOGIC
BOOT
HS CURRENT
SENSE
1.0V
Reference
ERROR
AMPLIFIER
FB
+
-
PG
+
-
PWM
COMP.
CONTROL
LOGIC
PFM MODE
CONTROL
SW
DRIVER
LS CURRENT
SENSE
POWER GOOD
CONTROL
AGND
PGND
8.3 Feature Description
8.3.1 Power-Good Flag Output
The power-good flag function (PG output pin) of the LMR34206-Q1 can be used to reset a system
microprocessor whenever the output voltage is out of regulation. This open-drain output goes low under fault
conditions, such as current limit and thermal shutdown, as well as 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 lasting less than tPG do not trip the power-good flag. Power-good operation can best be
understood by reference to Figure 9 and Figure 10. Note that during initial power-up a delay of about 4 ms
(typical) is inserted from the time that EN is asserted to the time that the power-good flag goes high. This delay
only occurs during start-up and is not encountered during normal operation of the power-good function.
The power-good output consists of an open drain NMOS; requiring an external pullup resistor to a suitable logic
supply. It can also be pulled up to either VCC or VOUT, through an appropriate resistor, as desired. If this function
is not needed, the PG pin must be grounded. 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 ≥ 2 V (typical). Limit the current into this pin to ≤ 4
mA.
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Feature Description (continued)
VOUT
VPG-HIGH_UP (107%)
VPG-HIGH-DN (105%)
VPG-LOW-UP (95%)
VPG-LOW-DN (93%)
PG
High = Power Good
Low = Fault
Figure 9. Static Power-Good Operation
12
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Feature Description (continued)
Glitches do not cause false operation nor reset timer
VOUT
VPG-LOW-UP (95%)
VPG-LOW-DN (93%)
<tPG
PG
tPG
tPG
tPG
Figure 10. Power-Good-Timing Behavior
8.3.2 Enable and Start-up
Start-up and shutdown are controlled by the EN input. This input features precision thresholds, allowing the use
of an external voltage divider to provide an adjustable input UVLO (see the External UVLO section). Applying a
voltage of ≥ VEN-VCC-H causes the device to enter standby mode, powering the internal VCC, but not producing an
output voltage. Increasing the EN voltage to VEN-OUT-H (VEN-H in Figure 11) fully enables the device, allowing it to
enter start-up mode and beginning the soft-start period. When the EN input is brought below VEN-OUT-H (VEN-H in
Figure 11) by VEN-OUT-HYS (VEN-HYS in Figure 11), the regulator stops running and enters standby mode. Further
decrease in the EN voltage to below VEN-VCC-L completely shuts down the device. This behavior is shown in
Figure 11. The EN input may be connected directly to VIN if this feature is not needed. This input must not be
allowed to float. The values for the various EN thresholds can be found in the table.
The LMR34206-Q1 utilizes a reference-based soft start that prevents output voltage overshoots and large inrush
currents as the regulator is starting up. A typical start-up waveform is shown in Figure 12 along with typical
timings. The rise time of the output voltage is about 4 ms.
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Feature Description (continued)
EN
VEN-H
VEN-H ± VEN-HYS
VEN-VCC-H
VEN-VCC-L
VCC
5V
0
VOUT
VOUT
0
Figure 11. Precision Enable Behavior
14
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Feature Description (continued)
Figure 12. Typical Start-up Behavior
VIN = 12V, VOUT = 3.3 V, IOUT = 0.6 A
8.3.3 Current Limit and Short Circuit
The LMR34206-Q1 incorporates valley current limit for normal overloads and for short-circuit protection. In
addition the high-side power MOSFET is protected from excessive current by a peak current limit circuit. Cycleby-cycle current limit is used for overloads, while hiccup mode is used for short circuits. Finally, a zero current
detector is used on the low-side power MOSFET to implement diode emulation mode (DEM) at light loads (see
Glossary).
During overloads the low-side current limit, ILIMIT, determines the maximum load current that the LMR34206-Q1
can supply. When the low-side switch turns on, the inductor current begins to ramp down. If the current does not
fall below ILIMIT before the next turnon cycle, then that cycle is skipped, and the low-side MOSFET is left on until
the current falls below ILIMIT. This is somewhat different than the more typical peak current limit and results in
Equation 1 for the maximum load current.
IOUT
max
ILIMIT
VIN VOUT VOUT
˜
2 ˜ fSW ˜ L
VIN
where
•
•
fSW = switching frequency
L = inductor value
(1)
If, during current limit, the voltage on the FB input falls below about 0.4 V due to a short circuit, the device enters
into hiccup mode. In this mode the device stops switching for tHC or about 94 ms, and then goes through a
normal re-start with soft start. If the short-circuit condition remains, the device runs in current limit for about 20
ms (typical) and then shuts down again. This cycle repeats, as shown in as long as the short-circuit condition
persists. This mode of operation helps to reduce the temperature rise of the device during a hard short on the
output. Of course the output current is greatly reduced during hiccup mode. Once the output short is removed
and the hiccup delay is passed, the output voltage recovers normally as shown in Figure 13.
The high-side-current limit trips when the peak inductor current reaches ISC. This is a cycle-by-cycle current limit
and does not produce any frequency or load current fold back. It is meant to protect the high-side MOSFET from
excessive current. Under some conditions, such as high input voltages, this current limit may trip before the lowside protection. Under this condition, ISC determines the maximum output current. Note that ISC varies with duty
cycle.
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Feature Description (continued)
Figure 13. Short-Circuit Transient and Recovery
8.3.4 Undervoltage Lockout and Thermal Shutdown
The LMR34206-Q1 incorporates an undervoltage-lockout feature on the output of the internal LDO (at the VCC
pin). When VCC reaches 3.8 V (typ.), the device receives the EN signal and starts switching. When VCC falls
below 3.3 V (typ.), the device shuts down, regardless of EN status. Because the LDO is in dropout during these
transitions, the previously mentioned values roughly represent the input voltage levels during the transitions.
Thermal shutdown is provided to protect the regulator from excessive junction temperature. When the junction
temperature reaches about 170°C, the device shuts down; re-start occurs when the temperature falls to about
158°C .
8.4 Device Functional Modes
8.4.1 Auto Mode
In auto mode the device moves between PWM and PFM as the load changes. At light loads the regulator
operates in PFM. At higher loads the mode changes to PWM.
In PWM the regulator operates as a constant frequency, current mode, full synchronous converter using PWM to
regulate the output voltage. While operating in this mode the output voltage is regulated by switching at a
constant frequency and modulating the duty cycle to control the power to the load. This provides excellent line
and load regulation and low output voltage ripple.
In PFM the high-side MOSFET is turned on in a burst of one or more pulses to provide energy to the load. The
duration of the burst depends on how long it takes the inductor current to reach IPEAK-MIN. The frequency of these
bursts is adjusted to regulate the output, while diode emulation (DEM) is used to maximize efficiency (see
Glossary). This mode provides high light-load efficiency by reducing the amount of input supply current required
to regulate the output voltage at small loads. This trades off very good light-load efficiency for larger output
voltage ripple and variable switching frequency. Also, a small increase in output voltage occurs at light loads. The
actual switching frequency and output voltage ripple depends on the input voltage, output voltage, and load.
Typical switching waveforms in PFM and PWM are shown in Figure 14 and Figure 15.
16
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Device Functional Modes (continued)
Figure 14. Typical PFM Switching Waveforms
VIN = 12 V, VOUT = 3.3 V, IOUT = 30 mA
Figure 15. Typical PWM Switching Waveforms
VIN = 12 V, VOUT = 3.3 V, IOUT = 0.6 A, ƒS = 2100 kHz
8.4.2 Forced PWM Operation
The following select variant(s) is/are a factory option made available for cases when constant frequency
operation is more important than light load efficiency.
Table 1. LMR34206-Q1 Device Variants with Fixed Frequency Operation at No Load
ORDERABLE PART NUMBER
OUTPUT VOLTAGE
SPREAD SPECTRUM
FPWM
FSW
LMR34206FSC3RNXTQ1
3.3-V fixed
Yes
Yes
2.1 MHz
LMR34206FSC3RNXRQ1
3.3-V fixed
Yes
Yes
2.1 MHz
LMR34206FSC5RNXTQ1
5-V fixed
Yes
Yes
2.1 MHz
LMR34206FSC5RNXRQ1
5-V fixed
Yes
Yes
2.1 MHz
In FPWM operation, the diode emulation feature is turned off. This means that the device remains in CCM under
light loads. Under conditions where the device must reduce the on-time or off-time below the ensured minimum
to maintain regulation, the frequency reduces to maintain the effective duty cycle required for regulation. This
occurs for very high and very low input/output voltage ratios. When in FPWM mode, a limited reverse current is
allowed through the inductor allowing power to pass from the regulator’s output to its input. Note that in FPWM
mode, larger currents pass through the inductor, if lightly loaded, than in auto mode. Once loads are heavy
enough to necessitate CCM operation, FPWM mode has no measurable effect on regulator operation.
8.4.3 Dropout
The dropout performance of any buck regulator is affected by the RDSON of the power MOSFETs, the DC
resistance of the inductor, and the maximum duty cycle that the controller can achieve. As the input voltage is
reduced to near the output voltage, the off-time of the high-side MOSFET starts to approach the minimum value.
Beyond this point the switching may become erratic and/or the output voltage falls out of regulation. To avoid this
problem the LMR34206-Q1 automatically reduces the switching frequency to increase the effective duty cycle
and maintain regulation. In this data sheet the dropout voltage is defined as the difference between the input and
output voltage when the output has dropped by 1% of its nominal value. Under this condition the switching
frequency has dropped to its minimum value of about 140 kHz. Note that the 0.4 V short circuit detection
threshold is not activated when in dropout mode. Typical dropout characteristics can be found in Figure 16 and
Figure 17.
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2.5E+6
7
IOUT = 300 mA
IOUT = 600 mA
2.25E+6
Switching Frequency (Hz)
6.5
Output Voltage (V)
6
5.5
5
4.5
4
3.5
2E+6
1.75E+6
1.5E+6
1.25E+6
1E+6
7.5E+5
5E+5
IOUT = 300 mA
IOUT = 600 mA
2.5E+5
0
3
4
4.2
4.4
4.6
4.8
5
5.2
Input Voltage (V)
5.4
5.6
5.8
5
6
5.1
5.2
5.3
lmr3
Figure 16. Overall Dropout Characteristic
VOUT = 5 V
5.4 5.5 5.6
Input Voltage (V)
5.7
5.8
5.9
6
lmr3
Figure 17. Typical ƒSW vs Output Current
ƒSW = 2100 kHz
8.4.4 Minimum Switch On-Time
Every switching regulator has a minimum controllable on-time dictated by the inherent delays and blanking times
associated with the control circuits. This imposes a minimum switch duty cycle and therefore a minimum
conversion ratio. The constraint is encountered at high input voltages and low output voltages. To help extend
the minimum controllable duty cycle, the LMR34206-Q1 automatically reduces the switching frequency when the
minimum on-time limit is reached. In this way the converter can regulate the lowest programmable output voltage
at the maximum input voltage. An estimate for the approximate input voltage, for a given output voltage, before
frequency foldback occurs is found in Equation 2. As the input voltage is increased, the switch on-time (duty
cycle) reduces to regulate the output voltage. When the on-time reaches the limit, the switching frequency drops,
while the on-time remains fixed.
VOUT
VIN d
t ON ˜ fSW
(2)
2.4E+6
2.2E+6
Swithcing Frequency (Hz)
2E+6
1.8E+6
1.6E+6
1.4E+6
1.2E+6
1E+6
8E+5
6E+5
4E+5
IOUT = 300 mA
IOUT = 600 mA
2E+5
0
10
15
20
25
30
Input Voltage (V)
35
40
45
Freq
Figure 18. Switching Frequency vs Input Voltage
VOUT = 3.3 V
18
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8.4.5 Spread Spectrum Operation
The spread spectrum is a factory option in the select variants.
Table 2. LMR34206-Q1 Device Variant(s) with Spread Spectrum Operation
ORDERABLE PART NUMBER
OUTPUT VOLTAGE
SPREAD SPECTRUM
FPWM
fSW
LMR34206FSC3RNXTQ1
3.3-V Fixed
Yes
Yes
2.1 MHz
LMR34206FSC3RNXRQ1
3.3-V Fixed
Yes
Yes
2.1 MHz
LMR34206SC3QRNXTQ1
3.3-V Fixed
Yes
No
2.1 MHz
LMR34206SC3QRNXRQ1
3.3-V Fixed
Yes
No
2.1 MHz
LMR34206FSC5RNXTQ1
5-V Fixed
Yes
Yes
2.1 MHz
LMR34206FSC5RNXRQ1
5-V Fixed
Yes
Yes
2.1 MHz
LMR34206SC5QRNXTQ1
5-V Fixed
Yes
No
2.1 MHz
LMR34206SC5QRNXRQ1
5-V Fixed
Yes
No
2.1 MHz
The purpose of the spread spectrum is to eliminate peak emissions at specific frequencies by spreading
emissions across a wider range of frequencies than a part with fixed frequency operation. In most systems
containing the LMR34206-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. The LMR34206-Q1 devices with a triangular spread spectrum use typically a ±4% spreading rate
with the modulation rate set at 16 kHz (typical). The spread spectrum is only available while the internal clock is
free running at its natural frequency. Any of the following conditions overrides spread spectrum, turning it off:
• At high input voltages/low output voltage ratio when the device operates at minimum on time the internal
clock is slowed disabling spread spectrum.
• The clock is slowed during dropout.
• The internal clock is slowed at light load in the PFM variant (LMR34206SC3QRNXTQ1,
LMR34206SC5QRNXRQ1). In FPWM mode, spread spectrum is active even if there is no load.
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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 LMR34206-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 0.6 A. The following design procedure can be used to select
components for the LMR34206-Q1. Alternately, the WEBENCH® Design Tool may be used to generate a
complete design. This tool utilizes an iterative design procedure and has access to a comprehensive database of
components. This allows the tool to create an optimized design and allows the user to experiment with various
options.
9.2 Typical Application
Figure 19 shows for the LMR34206-Q1. This device is designed to function over 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 a range of the most common output voltages.
L
VIN
CIN
4.7 µF
CHF1
220 nF
VIN
CHF2
220 nF
VOUT
SW
VIN
CBOOT
COUT
BOOT
EN
VPU
0.1 µF
LMR34206-Q1
100 NŸ
PG
FB
VCC
CVCC
1 µF
PGND
PGND
AGND
Figure 19. Example Applications Circuit (Fixed Output)
Table 3. Typical External Component Values
ƒSW (kHz)
VOUT (V)
L (µH)
Nominal COUT (rated
capacitance) (1)
Minimum COUT (rated
capacitance) (2)
CIN
2100
3.3
6.8
2 × 15 µF
1 × 15 µF
4.7 µF + 2 × 220 nF
2100
5
10
2 × 15 µF
1 × 15 µF
4.7 µF + 2 × 220 nF
(1)
(2)
20
Optimized for superior load transient performance from 0 to 100% rated load.
Optimized for size constrained end applications.
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9.2.1 Design Requirements
9.2.1.1 Design Requirements
Example requirements for a typical 3.3-V application. The input voltages are here for illustration purposes only.
See Specifications for the operating input voltage range.
Table 4. Detailed Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage
6 V to 18 V steady state, 4.2 V to 42-V transients
Output voltage
3.3 V
Maximum output current
0 A to 0.6 A
Switching frequency
2100 kHz
Current consumption at 0-A load
Not Critical: <100 mA is acceptable
Switching frequency at 0-A load
Not critical: Need fixed frequency operation at high load only
Table 5. List of Components
VOUT
FREQUENCY
COUT
L
U1
3.3 V
2100 kHz
1 × 15 µF
7.8 µH, 13.6 mΩ
LMR34206FSC3RNXRQ1
9.2.2 Detailed Design Procedure
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 the use of smaller inductors and output capacitors, and hence a
more compact design. For this example 2.1 MHz is used.
9.2.2.2 Setting the Output Voltage
FB is connected directly to the output voltage node. Preferably, near the top of the output capacitor. If the
feedback point is located further away from the output capacitors (that is, remote sensing), then a small 100-nF
capacitor may be needed at the sensing point.
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. Note that when selecting the ripple current for applications with much smaller maximum load than the
maximum available from the device, use the the maximum device current. Equation 3 can be used to determine
the value of inductance. The constant K is the percentage of inductor current ripple. For this example K = 0.4
was chosen with an inductance 5.1 µH; the standard value of 7.8 µH was selected.
L
VIN VOUT
V
˜ OUT
fSW ˜ K ˜ IOUT max VIN
(3)
Ideally, the saturation current rating of the inductor is at least as large as the high-side switch current limit, ISC.
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, ILIMIT, is designed to reduce the risk of current runaway, a saturated inductor can
cause the current to rise to high values very rapidly. This may 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. Powered iron cores exhibit a soft saturation, allowing some
relaxation in the current rating of the inductor. However, they have more core losses at frequencies above about
1 MHz. In any case, the inductor saturation current must not be less than the device low-side current limit, ILIMIT.
In order to avoid sub-harmonic oscillation, the inductance value must not be less than that given in Equation 4:
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VOUT
fSW
(4)
9.2.2.4 Output Capacitor Selection
The value of the output capacitor, and its ESR, determine the output voltage ripple and load transient
performance. The output capacitor bank is usually limited by the load transient requirements, rather than the
output voltage ripple. Equation 5 can be used to estimate a lower bound on the total output capacitance, and an
upper bound on the ESR, required to meet a specified load transient.
º
ª
'IOUT
K2
COUT t
˜«1 D ˜ 1 K
˜ 2 D»
12
fSW ˜ 'VOUT ˜ K «¬
»¼
ESR d
D
2 K ˜ 'VOUT
ª
2 ˜ 'IOUT «1 K
«¬
K2
12
§
1 ·º
¸¸»
˜ ¨¨1
© (1 D) ¹»¼
VOUT
VIN
where
•
•
•
ΔVOUT = output voltage transient
ΔIOUT = output current transient
K = Ripple factor from
(5)
Once the output capacitor and ESR have been calculated, Equation 6 can be used to check the output voltage
ripple.
Vr # 'IL ˜ ESR 2
1
8 ˜ fSW ˜ COUT
2
where
•
Vr = peak-to-peak output voltage ripple
(6)
The output capacitor and ESR can then be adjusted to meet both the load transient and output ripple
requirements.
In practice the output capacitor has the most influence on the transient response and loop phase margin. Load
transient testing and bode plots are the best way to validate any given design and must always be completed
before the application goes into production. In addition to the required output capacitance, a small ceramic
placed on the output can help to reduce high frequency noise. Small case size ceramic capacitors in the range of
1 nF to 100 nF can be very helpful in reducing spikes on the output caused by inductor and board parasitics.
Limit the maximum value of total output capacitance to about 10 times the design value, or 1000 µF, whichever
is smaller. Large values of output capacitance can adversely affect the start-up behavior of the regulator as well
as the loop stability. If values larger than noted here must be used, then a careful study of start-up at full load
and loop stability must be performed.
22
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9.2.2.5 Input Capacitor Selection
The ceramic input capacitors provide a low impedance source to the regulator in addition to supplying the ripple
current and isolating switching noise from other circuits. A minimum ceramic capacitance of 4.7-µF is required on
the input of the LMR34206-Q1. 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/or maintain the input voltage during load transients. In addition a small case size 220-nF
ceramic capacitor must be used at the input, as close a possible to the regulator. This provides a high frequency
bypass for the control circuits internal to the device. For this example a 4.7-µF, 50-V, X7R (or better) ceramic
capacitor is chosen. The 220 nF must also be rated at 50-V with an X7R dielectric. The VQFN 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, place two 220-nF ceramic capacitors at each VIN-PGND
location.
It is often desirable to use an electrolytic capacitor on the input in parallel with the ceramics. This is especially
true if long leads/traces are used to connect the input supply to the regulator. 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 voltage dips caused by input supplies with unusually high impedance.
Most of the input switching current passes through the ceramic input capacitor(s). The approximate RMS value of
this current can be calculated from Equation 7 and should be checked against the manufacturers' maximum
ratings.
I
IRMS # OUT
2
(7)
9.2.2.6 CBOOT
The LMR34206-Q1 requires a bootstrap capacitor connected between the BOOT pin and the SW pin. This
capacitor stores energy that is used to supply the gate drivers for the power MOSFETs. A high-quality ceramic
capacitor of 100 nF and at least 16 V is required.
9.2.2.7 VCC
The VCC pin is the output of the internal LDO used to supply the control circuits of the regulator. This output
requires a 1-µF, 16-V ceramic capacitor connected from VCC to GND for proper operation. In general this output
must not be loaded with any external circuitry. However, this output can be used to supply the pullup for the
power-good function (see Power-Good Flag Output). A value in the range of 10 kΩ to 100 kΩ is a good choice in
this case. The nominal output voltage on VCC is 5 V.
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9.2.2.8 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 20 can be used. 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 and then Equation 8 is used to calculate RENT and VOFF.
VIN
RENT
EN
RENB
Figure 20. Set-up for External UVLO Application
RENT
§ VON
¨¨
© VEN H
VOFF
§
VEN HYS
VON ˜ ¨¨1
VEN
©
·
1¸¸ ˜ RENB
¹
·
¸¸
¹
where
•
•
24
VON = VIN turnon voltage
VOFF = VIN turnoff voltage
(8)
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9.2.2.9 Maximum Ambient Temperature
As with any power conversion device, the LMR34206-Q1 dissipates internal power while operating. The effect of
this power dissipation is to raise the internal temperature of the converter above ambient. The internal die
temperature (TJ) is a function of the ambient temperature, the power loss and the effective thermal resistance,
RθJA of the device and PCB combination. The maximum internal die temperature for the LMR34206-Q1 must be
limited to 150°C. This establishes a limit on the maximum device power dissipation and therefore the load
current. Equation 9 shows the relationships between the important parameters. It is easy to see that larger
ambient temperatures (TA) and larger values of RθJA reduce the maximum available output current. The converter
efficiency can be estimated by using the curves provided in this data sheet. If the desired operating conditions
cannot be found in one of the curves, then interpolation can be used to estimate the efficiency. Alternatively, the
EVM can be adjusted to match the desired application requirements and the efficiency can be measured directly.
The correct value of RθJA is more difficult to estimate. As stated in Semiconductor and IC Package Thermal
Metrics, the values given in are not valid for design purposes and must not be used to estimate the thermal
performance of the application. The values reported in that table were measured under a specific set of
conditions that are rarely obtained in an actual application.
IOUT
MAX
TJ TA
1
K
˜
˜
R TJA
1 K VOUT
where
•
η = Efficiency
(9)
The effective RθJA is a critical parameter and depends on many factors such as power dissipation, air
temperature/flow, PCB area, copper heat-sink area, number of thermal vias under the package, and adjacent
component placement; to mention just a few. Due to the ultra-miniature size of the VQFN (RNX) package, a DAP
is not available. This means that this package exhibits a somewhat greater RθJA. A typical example of RθJA vs
copper board area can be found in Figure 21. Note that the data given in this graph is for illustration purposes
only, and the actual performance in any given application depends on all of the factors mentioned above.
70
60
55
R
JA (ƒC/w)
65
50
45
RNX, 4L
40
0
10
20
30
40
50
Copper Area (cm2)
60
70
C005
Figure 21. RθJA versus Copper Board Area for the VQFN (RNX) Package
Use the following resources as guides to optimal thermal PCB design and estimating RθJA for a given application
environment:
• Thermal Design by Insight not Hindsight
• Semiconductor and IC Package Thermal Metrics
• Thermal Design Made Simple with LM43603 and LM43602
• Using New Thermal Metrics
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9.2.3 Application Curves
Unless otherwise specified the following conditions apply: VIN = 12 V, TA = 25°C. The circuit is shown in
Figure 19, with the BOM from Table 5. through Figure 36 show the conducted and radiated emissions
performance tested against the CISPR25 Class 5 limits. For the conducted EMI results the limit lines labeled
"AV5" represent the average limits, and the limit lines labeled "PK5" represent the peak limits. For the radiated
EMI results the blue limit lines represent the average limits, and the black limit lines represent the peak limits.
100%
3.38
90%
3.36
80%
3.34
Output Voltage (V)
Efficiency
70%
60%
50%
40%
30%
3.32
3.3
3.28
3.26
20%
6 VIN
12 VIN
18 VIN
10%
6 VIN
12 VIN
18 VIN
3.24
0
3.22
0
0.1
0.2
0.3
0.4
Output Current (A)
VOUT = 3.3 V
0.5
0.6
0
0.1
2100 kHz
VOUT = 3.3 V
Figure 22. Efficiency
24
2.2E+6
23
Input Supply Current (mA)
Swithcing Frequency (Hz)
2E+6
1.8E+6
1.6E+6
1.4E+6
1.2E+6
1E+6
8E+5
6E+5
4E+5
IOUT = 300 mA
IOUT = 600 mA
2E+5
0.6
D009
2100 kHz
22
21
20
19
18
17
16
15
14
15
20
VOUT = 3.3 V
25
30
35
40
Input Voltage (V)
45
50
55
60
5
10
VOUT = 3.3 V
Slew Rate = 1 A/µs
2100 kHz
2100 kHz
15
Freq
VOUT = 3.3 V
Figure 24. Switching Frequency vs Input Voltage
ILOAD= 10 mA - 0.3 A
20
25 30 35 40
Input Voltage (V)
45
50
55
60
iqvi
2100 kHz
Figure 25. Input Supply Current
VOUT = 3.3 V
Slew Rate = 1 A/µs
Figure 26. Load Transient
26
0.5
Figure 23. Load Regulation
2.4E+6
0
10
0.2
0.3
0.4
Output Current (A)
D007
2100 kHz
ILOAD= 10 mA - 0.6 A
Figure 27. Load Transient
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VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 150kHz to 30 MHz
IOUT = 1.5 A
Figure 28. Conducted EMI vs. CISPR25 Limits (Yellow:
Peak Signal, Blue: Average Signal)
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 150 kHz to 30 MHz
IOUT = 1.5 A
Figure 30. Radiated EMI Rod vs. CISPR25 Limits
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 30 MHz to 200 MHz
IOUT = 1.5 A
Figure 32. Radiated EMI Bicon Horizontal vs. CISPR25
Limits
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 30 MHz to 108 MHz
IOUT = 1.5 A
Figure 29. Conducted EMI vs. CISPR25 Limits (Yellow:
Peak Signal, Blue: Average Signal)
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 30 MHz to 200 MHz
IOUT = 1.5 A
Figure 31. Radiated EMI Bicon Vertical vs. CISPR25 Limits
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 200 MHz to 1 GHz
IOUT = 1.5 A
Figure 33. Radiated EMI Log Vertical vs. CISPR25 Limits
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VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 200 MHz to 1 GHz
www.ti.com
IOUT = 1.5 A
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 1.83 GHz to 2.5 GHz
IOUT = 1.5 A
Figure 35. Radiated EMI Horn Vertical vs. CISPR25 Limits
Figure 34. Radiated EMI Log Horizontal vs. CISPR25 Limits
83H9652
VIN
IN+
FB1
+
CD = 100 uF
GND
IN±
CF1 = 4.7 uF
VIN = 13.5 V
VOUT = 5 V
Frequency Tested: 1.8 GHz to 2.5 GHz
IOUT = 1.5 A
Figure 36. Radiated EMI Horn Horizontal vs. CISPR25
Limits
28
CF2 = 0.1 uF
CF3 = 4.7 uF
Figure 37. Recommended Input EMI Filter
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10 Power Supply Recommendations
The characteristics of the input supply must be compatible with the Specifications found in this data sheet. In
addition, the input supply must be capable of delivering the required input current to the loaded regulator. The
average input current can be estimated with Equation 10.
VOUT ˜ IOUT
IIN
VIN ˜ K
where
•
η is the efficiency
(10)
If the regulator 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 regulator. The parasitic inductance, in combination with the low-ESR, ceramic input
capacitors, can form an underdamped resonant circuit, resulting in overvoltage transients at the input to the
regulator. 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 may cause the
regulator to momentarily shutdown and/or reset. The best way to solve these kind of issues is to reduce the
distance from the input supply to the regulator and/or use an aluminum or tantalum input capacitor in parallel with
the ceramics. The moderate ESR of these types of capacitors help to damp the input resonant circuit and reduce
any overshoots. A value in the range of 20 µF to 100 µF is usually sufficient to provide input damping and help to
hold the input voltage steady during large load transients.
Sometimes, for other system considerations, an input filter is used in front of the regulator. This can lead to
instability, as well as some of the effects mentioned above, unless it is designed carefully. The AN-2162 Simple
Success With Conducted EMI From DCDC Converters User's Guide provides helpful suggestions when
designing an input filter for any switching regulator.
In some cases a transient voltage suppressor (TVS) is used on the input of regulators. 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 regulator, the output capacitors discharge through the device back to the input. This
uncontrolled current flow may damage the device.
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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. Poor 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, to a great extent the EMI performance of the regulator is dependent on the PCB layout. In a buck
converter the most critical PCB feature is the loop formed by the input capacitor(s) and power ground, as shown
in Figure 38. 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. shows a recommended layout for the critical components of the .
1. Place the input capacitor(s) as close as possible to the VIN and GND terminals. VIN and GND pins are
adjacent, simplifying the input capacitor placement.
2. Place bypass capacitor for VCC close to the VCC pin. This capacitor must be placed close to the device and
routed with short, wide traces to the VCC and GND pins.
3. Use wide traces for the CBOOT capacitor. Place CBOOT close to the device with short/wide traces to the BOOT
and SW pins. Route the SW pin to the N/C pin and used to connect the BOOT capacitor to SW.
4. 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 GND 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 regulator.
5. Use at least one ground plane in one of the middle layers. This plane acts as a noise shield and also act as
a heat dissipation path.
6. Provide wide paths for VIN, VOUT, and GND. Making these paths as wide and direct as possible reduces
any voltage drops on the input or output paths of the converter and maximizes efficiency.
7. Provide enough PCB area for proper heat-sinking. As stated in the section, enough copper area must be
used to ensure a low RθJA, commensurate with the maximum load current and ambient temperature. The top
and bottom PCB layers must be made with two ounce copper; and no less than one ounce. If the PCB
design uses multiple copper layers (recommended), these thermal vias can also be connected to the inner
layer heat-spreading ground planes.
8. 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.
See the following PCB layout resources for additional important guidelines:
• Layout Guidelines for Switching Power Supplies Application Report
• Simple Switcher PCB Layout Guidelines Application Report
• Construction Your Power Supply- Layout Considerations Seminar
• Low Radiated EMI Layout Made Simple with LM4360x and LM4600x Application Report
30
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Layout Guidelines (continued)
VIN
CIN
SW
GND
Figure 38. Current Loops with Fast Edges
11.1.1 Ground and Thermal Considerations
As previously mentioned, TI recommends using one of the middle layers as a solid ground plane. A ground plane
provides shielding for sensitive circuits and traces as well as a quiet reference potential for the control circuitry.
Connect the AGND and PGND pins 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 may 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; use for sensitive routes.
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
VOUT
VOUT
INDUCTOR
COUT
COUT
GND
GND
CIN
CHF
12
CBOOT
1
VIN
CHF
11
2
10
3
9
EN
4
8
PGOOD
5
6
VIN
7
CVCC
GND
HEATSINK
GND
HEATSINK
INNER GND PLANE
Top Trace/Plane
Inner GND Plane
VIN Strap on Inner Layer
VIA to Signal Layer
VIA to GND Planes
VIA to VIN Strap
Top
Inner GND Plane
VIN Strap and
GND Plane
Signal
traces and
GND Plane
Trace on Signal Layer
Figure 39. Example Layout
32
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Development Support
• Two-Stage Power Supply Reference Design for Field Transmitters
• Wide Vin Power Supply Reference Design for Space-Constrained Industrial Sensors
• Automotive ADAS camera power supply reference design optimized for solution size and low noise
• How a DC/DC converter package and pinout design can enhance automotive EMI performance
• Introduction to Buck Converters Features: UVLO, Enable, Soft Start, Power Good
• Introduction to Buck Converters: Understanding Mode Transitions
• Introduction to Buck Converters: Minimum On-time and Minimum Off-time Operation
• Introduction to Buck Converters: Understanding Quiescent Current Specifications
• Trade-offs between thermal performance and small solution size with DC/DC converters
• Reduce EMI and shrink solution size with Hot Rod packaging
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation see the following:
• Texas Instruments, Designing High-Performance, Low-EMI Automotive Power Supplies Application Report
• Texas Instruments, Simple Switcher PCB Layout Guidelines Application Report
• Texas Instruments, Construction Your Power Supply- Layout Considerations Application Report
• Texas Instruments, Low Radiated EMI Layout Made Simple with LM4360x and LM4600x Application Report
• Texas Instruments, Semiconductor and IC Package Thermal Metrics Application Report
• Texas Instruments, Thermal Design Made Simple with LM43603 and LM43602 Application Report
12.3 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.
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12.4 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.
12.5 Trademarks
Hotrod, HotRod, E2E are trademarks of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.6 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.7 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.
34
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PACKAGE OPTION ADDENDUM
www.ti.com
3-Oct-2019
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LMR34206FSC3RNXRQ1
ACTIVE
VQFN-HR
RNX
12
3000
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426FC3
LMR34206FSC3RNXTQ1
ACTIVE
VQFN-HR
RNX
12
250
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426FC3
LMR34206FSC5RNXRQ1
ACTIVE
VQFN-HR
RNX
12
3000
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426FC5
LMR34206FSC5RNXTQ1
ACTIVE
VQFN-HR
RNX
12
250
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426FC5
LMR34206SC3QRNXRQ1
ACTIVE
VQFN-HR
RNX
12
3000
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426SC3
LMR34206SC3QRNXTQ1
ACTIVE
VQFN-HR
RNX
12
250
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426SC3
LMR34206SC5QRNXRQ1
ACTIVE
VQFN-HR
RNX
12
3000
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426SC5
LMR34206SC5QRNXTQ1
ACTIVE
VQFN-HR
RNX
12
250
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 125
426SC5
(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.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
3-Oct-2019
(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 2
PACKAGE MATERIALS INFORMATION
www.ti.com
30-Oct-2019
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LMR34206FSC3RNXRQ1 VQFNHR
RNX
12
3000
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206FSC3RNXTQ1
VQFNHR
RNX
12
250
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206FSC5RNXRQ1 VQFNHR
RNX
12
3000
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206FSC5RNXTQ1
VQFNHR
RNX
12
250
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206SC3QRNXRQ1 VQFNHR
RNX
12
3000
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206SC3QRNXTQ1 VQFNHR
RNX
12
250
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206SC5QRNXRQ1 VQFNHR
RNX
12
3000
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
LMR34206SC5QRNXTQ1 VQFNHR
RNX
12
250
180.0
8.4
2.3
3.2
1.0
4.0
8.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
30-Oct-2019
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LMR34206FSC3RNXRQ1
VQFN-HR
RNX
12
3000
195.0
200.0
45.0
LMR34206FSC3RNXTQ1
VQFN-HR
RNX
12
250
195.0
200.0
45.0
LMR34206FSC5RNXRQ1
VQFN-HR
RNX
12
3000
195.0
200.0
45.0
LMR34206FSC5RNXTQ1
VQFN-HR
RNX
12
250
195.0
200.0
45.0
LMR34206SC3QRNXRQ1
VQFN-HR
RNX
12
3000
195.0
200.0
45.0
LMR34206SC3QRNXTQ1
VQFN-HR
RNX
12
250
195.0
200.0
45.0
LMR34206SC5QRNXRQ1
VQFN-HR
RNX
12
3000
195.0
200.0
45.0
LMR34206SC5QRNXTQ1
VQFN-HR
RNX
12
250
195.0
200.0
45.0
Pack Materials-Page 2
GENERIC PACKAGE VIEW
RNX 12
2 x 3 mm, 0.5 mm pitch
VQFN-HR - 1 mm max height
PLASTIC QUAD FLATPACK-NO LEAD
Images above are just a representation of the package family, actual package may vary.
Refer to the product data sheet for package details.
4224286/A
PACKAGE OUTLINE
RNX0012B
VQFN-HR - 0.9 mm max height
SCALE 4.500
PLASTIC QUAD FLATPACK - NO LEAD
2.1
1.9
B
A
PIN 1 INDEX AREA
3.1
2.9
0.1 MIN
(0.05)
SECTION A-A
A-A 40.000
TYPICAL
0.9
0.8
C
SEATING PLANE
0.05
0.00
0.08 C
1
SYMM
(0.2) TYP
7
5
2X
0.675
2X
1.125
4X 0.5
8
4
PKG
1.725
1.525
2X
0.65
A
1
11
A
12
PIN 1 ID
11X
0.3
0.2
11X
0.5
0.3
0.3
0.2
0.1
0.05
C B A
C
4223969/C 10/2018
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.
3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.
www.ti.com
EXAMPLE BOARD LAYOUT
RNX0012B
VQFN-HR - 0.9 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
(0.25)
12
11X (0.6)
1
11
2X (0.65)
11X
(0.25)
(1.825)
2X
(1.125)
(0.788)
PKG
2X
(0.675)
4X (0.5)
8
4
(1.4)
(R0.05) TYP
5
SYMM
7
(1.8)
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE:25X
0.07 MAX
ALL AROUND
0.07 MIN
ALL AROUND
SOLDER MASK
OPENING
METAL EDGE
EXPOSED
METAL
SOLDER MASK
OPENING
EXPOSED
METAL
NON SOLDER MASK
DEFINED
(PREFERRED)
METAL
SOLDER MASK
DEFINED
PADS 1, 2, 10-12
SOLDER MASK DETAILS
4223969/C 10/2018
NOTES: (continued)
4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
www.ti.com
EXAMPLE STENCIL DESIGN
RNX0012B
VQFN-HR - 0.9 mm max height
PLASTIC QUAD FLATPACK - NO LEAD
2X (0.25)
2X (0.812)
12
11X (0.6)
11X (0.25)
1
11
2X
(0.65)
EXPOSED METAL
(1.294)
2X
(1.125)
PKG
(0.282)
2X (0.675)
4X (0.5)
8
4
(1.4)
(R0.05) TYP
5
SYMM
7
(1.8)
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
FOR PAD 12
87.7% PRINTED SOLDER COVERAGE BY AREA
SCALE:25X
4223969/C 10/2018
NOTES: (continued)
5. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
www.ti.com
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