Texas Instruments | TPS54478 2.95-V to 6-V Input, 4-A Synchrns Step-Down SWIFT™ Cnvrtr w/ Hiccup (Rev. B) | Datasheet | Texas Instruments TPS54478 2.95-V to 6-V Input, 4-A Synchrns Step-Down SWIFT™ Cnvrtr w/ Hiccup (Rev. B) Datasheet

Texas Instruments TPS54478 2.95-V to 6-V Input, 4-A Synchrns Step-Down SWIFT™ Cnvrtr w/ Hiccup (Rev. B) Datasheet
Product
Folder
Order
Now
Support &
Community
Tools &
Software
Technical
Documents
Reference
Design
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
TPS54478 2.95-V to 6-V Input, 4-A Synchronous Step-Down SWIFT™ Converter
With Hiccup Current Limit
1 Features
3 Description
•
The TPS54478 device is a full featured 6-V, 4-A,
synchronous step down current mode converter with
two integrated MOSFETs.
1
•
•
•
•
•
•
•
•
•
•
Two 30-mΩ (typical) MOSFETs for High Efficiency
at 4-A Loads
200-kHz to 2-MHz Switching Frequency
0.6-V ± 1% Voltage Reference Over Temperature
(–40°C to +150°C)
Start-up With Prebiased Voltage
Synchronizes to External Clock
Adjustable Slow Start / Sequencing
UV and OV Power-Good Output
Cycle by Cycle Current Limit and Hiccup Current
Protection
Thermally Enhanced 3-mm × 3-mm 16-Pin WQFN
(RTE)
Pin Compatible to TPS54418
Create a Custom Design Using the TPS54478
With the WEBENCH® Power Designer
2 Applications
•
•
•
Low-Voltage, High-Density Power Systems
Point-of-Load Regulation for High Performance
DSPs, FPGAs, ASICs, and Microprocessors
Broadband, Networking, and Optical
Communications Infrastructure
Simplified Schematic
VIN
Undervoltage lockout is internally set at 2.6 V, but
can be increased by programming the threshold with
a resistor network on the enable pin. The output
voltage start-up ramp is controlled by the soft-start
pin. An open-drain power-good signal indicates the
output is within 93% to 107% of its nominal voltage.
Cycle-by-cycle current limit, hiccup overcurrent
protection, and thermal shutdown protect the device
during an overcurrent condition.
For more SWIFT™ documentation, see the TI
website at www.ti.com/swift.
Device Information(1)
PART NUMBER
BOOT
R4
The TPS54478 provides accurate regulation for a
variety of loads with an accurate ±1% voltage
reference (VREF) over temperature. Efficiency is
maximized through the integrated 30-mΩ MOSFETs
and 525-μA typical supply current. Using the enable
pin, shutdown supply current is reduced to 2.5 µA by
entering a shutdown mode.
CBOOT
VIN
CI
The TPS54478 enables small designs by integrating
the MOSFETs, implementing current mode control to
reduce external component count, reducing inductor
size by enabling up to 2-MHz switching frequency,
and minimizing the IC footprint with a small 3-mm ×
3-mm thermally enhanced WQFN package.
TPS54478
EN
LO
TPS54478
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
CO
R1
PWRGD
space
VSENSE
SS/TR
RT /CLK
COMP
Efficiency
R2
95
GND
AGND
POWERPAD
C ss
90
VIN = 5 V
85
VIN = 3.3 V
80
R3
Efficiency - %
RT
BODY SIZE (NOM)
3.00 mm × 3.00 mm
VOUT
PH
R5
PACKAGE
WQFN (16)
C1
75
70
65
Copyright © 2016, Texas Instruments Incorporated
60
FS = 1 MHz,
55
DCR = 6.8 mW,
VO = 1.8 V
50
0
0.5
1
1.5
2
2.5
IO - Output Current - A
3
3.5
4
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.
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
4
4
4
5
5
7
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 11
7.1
7.2
7.3
7.4
7.5
Overview .................................................................
Functional Block Diagram .......................................
Feature Description.................................................
Device Functional Modes........................................
Programming...........................................................
11
12
12
21
21
8
Application and Implementation ........................ 22
8.1 Application Information............................................ 22
8.2 Typical Application ................................................. 22
9 Power Supply Recommendations...................... 30
10 Layout................................................................... 31
10.1 Layout Guidelines ................................................. 31
10.2 Layout Example .................................................... 31
10.3 Power Dissipation Estimate .................................. 32
11 Device and Documentation Support ................. 33
11.1
11.2
11.3
11.4
11.5
11.6
11.7
Device Support ....................................................
Documentation Support .......................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
33
33
33
33
33
34
34
12 Mechanical, Packaging, and Orderable
Information ........................................................... 34
4 Revision History
Changes from Revision A (November 2016) to Revision B
•
Page
Update title to include key features; add links for WEBENCH; delete link to SwitcherPro tool ............................................ 1
Changes from Original (June 2011) to Revision A
Page
•
Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section. ................................................................................................. 1
•
Deleted Ordering Information table; see POA at the end of the datasheet. .......................................................................... 1
2
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
5 Pin Configuration and Functions
VIN
1
VIN
2
VIN
EN
PWRGD
BOOT
RTE Package
16-Pin WQFN
Top View
16
15
14
13
12
PH
11
PH
Exposed Thermal Pad
(17)
PH
GND
4
9
SS/TR
AGND
5
6
7
8
RT/CLK
10
COMP
3
VSENSE
GND
Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
AGND
5
—
Analog Ground should be electrically connected to GND close to the device.
BOOT
13
O
A bootstrap capacitor is required between BOOT and PH. If the voltage on this
capacitor is below the minimum required by the BOOT UVLO, the output is forced
to switch off until the capacitor is refreshed.
COMP
7
I/O
Error amplifier output, and input to the output switch current comparator. Connect
frequency compensation components to this pin.
EN
15
I
Enable pin, internal pull-up current source. Pull below 1.21 V to disable. Float to
enable. Can be used to set the on/off threshold (adjust UVLO) with two additional
resistors.
GND
3, 4
—
Power Ground. This pin should be electrically connected directly to the power pad
under the IC.
10, 11, 12
O
The source of the internal high side power MOSFET, and drain of the internal low
side (synchronous) rectifier MOSFET.
PWRGD
14
O
An open drain output; asserts low if output voltage is low due to thermal shutdown,
overcurrent, over/under-voltage or EN shut down.
RT/CLK
8
I
Resistor Timing or External Clock input pin.
SS/TR
9
I
Slow start and tracking. An external capacitor connected to this pin sets the output
voltage rise time. The SS provides higer charge current when SS is below 0.15V,
resulting in two slopes of the SS voltage.
This pin can also be used for tracking.
Thermal Pad
17
—
1, 2, 16
I
Input supply voltage, 2.95 V to 6 V.
6
I
Inverting node of the transconductance (gm) error amplifier.
PH
VIN
VSENSE
GND pin should be connected to the exposed thermal pad for proper operation.
This thermal pad should be connected to any internal PCB ground plane using
multiple vias for good thermal performance.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
3
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
6 Specifications
6.1 Absolute Maximum Ratings (1)
MIN
MAX
VIN
–0.3
7
EN
–0.3
7
BOOT
Input voltage
PH + 7
VSENSE
–0.3
3
COMP
–0.3
3
PWRGD
–0.3
7
SS/TR
–0.3
3
RT/CLK
–0.3
3.3
BOOT-PH
Output voltage
Sink current
V
7
PH
PH 10 ns Transient
Source current
UNIT
–0.6
7
–2
10
V
EN
100
RT/CLK
100
COMP
100
µA
PWRGD
10
mA
SS/TR
100
µA
µA
Junction Temperature, Tj
–40
150
°C
Storage Temperature, Tstg
–65
150
°C
(1)
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Electrical Characteristics is
not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per QSS 009-105 (JESD22-A114A) (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±500
UNIT
V
The human body model is a 100-pF capacitor discharged through a 1.5-kΩ resistor into each pin. The machine model is a 200-pF
capacitor discharged directly into each pin.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
Input Voltage Range
Output Current
Operating Junction Temperature Range, TJ
4
Submit Documentation Feedback
NOM
MAX
UNIT
2.95
6
V
0
4
A
–40
150
°C
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
6.4 Thermal Information
TPS54478
THERMAL METRIC (1) (2) (3)
RTE (WQFN)
UNIT
16 PINS
RθJA
Junction-to-ambient thermal resistance
49.1
°C/W
RθJC(top)
RθJB
Junction-to-case (top) thermal resistance
0.7
°C/W
Junction-to-board thermal resistance
21.8
°C/W
ψJT
Junction-to-top characterization parameter
50.7
°C/W
ψJB
Junction-to-board characterization parameter
7.5
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
21.8
°C/W
(1)
(2)
(3)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
Maximum power dissipation may be limited by overcurrent protection
Power rating at a specific ambient temperature TA should be determined with a junction temperature of 150°C. This is the point where
distortion starts to substantially increase. Thermal management of the PCB should strive to keep the junction temperature at or below
150°C for best performance and long-term reliability. See power dissipation estimate in application section of this data sheet for more
information.
6.5 Electrical Characteristics
TJ = –40°C to 150°C, VIN = 2.95 to 6 V (unless otherwise noted)
DESCRIPTION
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SUPPLY VOLTAGE (VIN PIN)
Operating input voltage
2.95
6.0
V
0.7
2.5
μA
VSENSE = 0.7 V, VIN = 5 V, 25°C, RT = 78.7 kΩ
525
700
μA
Rising
1.30
Falling
1.21
Input under voltage lockout threshold
No voltage hysteresis
2.6
Shutdown supply current
EN = 0 V, 25°C, 2.95 V ≤ VIN ≤ 6 V
Quiescent Current - Iq
V
ENABLE AND UVLO (EN PIN)
Enable threshold
Input current
Enable threshold + 50 mV
–3.4
Enable threshold – 50 mV
–0.64
V
μA
VOLTAGE REFERENCE (VSENSE PIN)
Voltage Reference
2.95 V ≤ VIN ≤ 6 V, –40°C <TJ < 150°C
0.594
0.600
0.606
BOOT-PH = 5 V
30
60
BOOT-PH = 3.3 V
37
70
VIN = 5 V
30
60
VIN = 3.3 V
37
70
V
MOSFET
High side switch resistance
Low side switch resistance
mΩ
mΩ
ERROR AMPLIFIER
Input current
7
nA
Error amplifier transconductance (gm)
–2 μA < I(COMP) < 2 μA, V(COMP) = 1 V
225
μmhos
Error amplifier transconductance (gm) during
slow start
–2 μA < I(COMP) < 2 μA, V(COMP) = 1 V,
Vsense = 0.4 V
77
μmhos
Error amplifier source/sink
V(COMP) = 1 V, 100 mV overdrive
COMP to Iswitch gm
±20
μA
14
A/V
CURRENT LIMIT
Current limit threshold
VIN = 6V, Fs = 500 KHz
Cycles before entering hiccup
Cycles of converter in off state during hiccup
Low side Fet reverse current limit
5.2
6.5
8.2
A
512
Cycles
16384
Cycles
3.1
A
165
°C
THERMAL SHUTDOWN
Thermal shutdown
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
5
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Electrical Characteristics (continued)
TJ = –40°C to 150°C, VIN = 2.95 to 6 V (unless otherwise noted)
DESCRIPTION
TEST CONDITIONS
MIN
Hysteresis
TYP
MAX
15
UNIT
°C
TIMING RESISTOR AND EXTERNAL CLOCK (RT/CLK PIN)
Switching frequency range using RT mode
Switching frequency
200
R(RT/CLK) = 78.7 kΩ
400
Switching frequency range using CLK mode
Minimum CLK pulse width
RT/CLK voltage
500
300
2000
kHz
600
kHz
2000
kHz
75
R(RT/CLK) = 78.7 kΩ
ns
0.5
RT/CLK high threshold
1.6
RT/CLK low threshold
0.4
V
2.2
V
0.6
V
RT/CLK falling edge to PH rising edge delay
Measure at 500 kHz with RT resistor in series
75
ns
PLL lock in time
Measure at 500 kHz
14
μs
PH (PH PIN)
Minimum On time
Minimum Off time
Rise Time
Fall Time
Measured at 50% points on PH, VIN = 5 V, IOUT = 2 A
100
Measured at 50% points on PH, VIN = 5 V,
IOUT = 0 A
120
Prior to skipping off pulses, VIN = 5 V,
IOUT = 2 A
110
VIN = 5 V, 4 A
ns
ns
1.5
V/ns
1.5
BOOT (BOOT PIN)
BOOT Charge Resistance
VIN = 5 V
15
Ω
BOOT-PH UVLO
VIN = 2.95 V
2.2
V
0.15
V
V(SS/TR) < VSSTHR
45
μA
V(SS/TR) > VSSTHR
2.2
SS/TR to VSENSE matching
V(SS/TR) = 0.3 V
65
SS/TR to reference crossover
98% normal
0.86
V
SS/TR discharge voltage (Overload)
VSENSE = 0 V
2.5
mV
SS/TR discharge current (Overload)
VSENSE = 0 V, V(SS/TR) = 0.4 V
900
µA
SS discharge current (UVLO, EN, Thermal
fault)
VIN = 5 V, V(SS) = 0.5 V
1.16
mA
SLOW START AND TRACKING (SS/TR PIN)
SS voltage threshold (VSSTHR)
Charge Current
mV
POWER GOOD (PWRGD PIN)
VSENSE falling (Fault)
VSENSE threshold
93
VSENSE rising (Good)
95
VSENSE rising (Fault)
107
VSENSE falling (Good)
105
% Vref
Hysteresis
VSENSE falling
2
Output high leakage
VSENSE = VREF, V(PWRGD) = 5.5 V
7
On resistance
VIN = 2.95 V
56
120
Ω
Output low
I(PWRGD) = 3 mA
0.2
0.3
V
Minimum VIN for valid output
V(PWRGD) < 0.5 V at 100 μA
1.2
1.6
V
6
Submit Documentation Feedback
% Vref
nA
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
6.6 Typical Characteristics
580
3
560
VIN = 5 V
Ivin - Supply Current - mA
Iq - Shutdown Supply Current - mA
570
2.5
2
VIN = 5 V
1.5
VIN = 3.3 V
1
550
540
530
VIN = 3.3 V
520
510
500
0.5
490
0
-50
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
480
-50
150
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 2. VIN Supply Current vs Temperature
Figure 1. Shutdown Supply Current vs Temperature
1.32
0
EN Pin Current @ Vin = 5 V, VEN = Threshold - 50 mV
EN Rising, Vin = 3.3 V
1.31
-0.5
1.3
1.29
-1
EN Rising, Vin = 5 V
EN - Pin Current - mA
EN - Threshold - V
1.28
1.27
1.26
1.25
1.24
1.23
EN Falling, Vin = 3.3 V
1.22
-1.5
-2
-2.5
EN Pin Current @ Vin = 5 V, VEN = Threshold + 50 mV
-3
1.21
1.2
-3.5
EN Falling, Vin = 5 V
1.19
1.18
-50
EN Pin Current @ Vin = 3.3 V, VEN = Threshold - 50 mV
EN Pin Current @ Vin = 3.3 V, VEN = Threshold + 50 mV
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
-4
-50
150
-25
Figure 3. EN Pin Voltage vs Temperature
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 4. EN Pin Current vs Temperature
60
0.606
RDSON - Top and Bottom MOSFET - W
0.605
Vref - Voltage Reference - V
0.604
0.603
VIN = 5 V
0.602
0.601
0.6
0.599
VIN = 3.3 V
0.598
0.597
0.596
55
High Side Rdson Vin = 3.3 V
50
Low Side Rdson Vin = 3.3 V
45
40
35
30
Low Side Rdson Vin = 5 V
25
0.595
0.594
-50
High Side Rdson Vin = 5 V
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
Figure 5. Voltage Reference vs Temperature
150
20
-50
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 6. MOSFET Rdson vs Temperature
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
7
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Typical Characteristics (continued)
7
HSFET Lim-High Side Fet Current Limit Current - A
310
EA - Transconductance - mA/V
290
VIN = 3.3 V
270
250
230
VIN = 5 V
210
190
170
-50
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 7. Transconductance vs Temperature
VIN = 5 V
6.5
VIN = 3.3 V
6
5.5
5
-50
-25
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 8. High Side FET Current Limit vs Temperature
2000
500
RT = 84 kW,
Vin = 5 V
1800
1600
fs - Switching Frequency - kHz
fs - Switching Frequency - kHz
0
1400
1200
1000
800
600
400
495
490
485
480
200
0
10
30
50
70
90
110
RT - Resistance - kW
130
475
-50
150
Figure 9. Switching Frequency vs RT Resistance
-40
0.159
-41
ISS1 - SS Charge Current - mA
SS Threshold Voltage - V
0.158
0.157
0.156
0.155
VIN = 5 V
0.154
0.153
0.152
0.151
0.15
-50
25
50
75
100
TJ - Junction Temperature - °C
125
150
-42
-43
Vin = 5 V, Vss < 0.15 V
-44
-45
-46
Vin = 3.3 V, Vss < 0.15 V
-47
-48
-49
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 11. VSS Voltage Threshold VSSTHR vs Temperature
8
0
Figure 10. Switching Frequency vs Temperature
0.16
VIN = 3.3 V
-25
-50
-50
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 12. SS Charge Current vs Temperature
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Typical Characteristics (continued)
100
-2
-2.1
Vin = 5 V; Vss = 0.4 V
90
RDSON - Power Good - W
ISS2 - SS Charge Current - mA
-2.2
-2.3
Vin = 3.3 V; Vss = 0.4 V
-2.4
-2.5
-2.6
-2.7
-2.8
80
70
VIN = 5 V
60
50
-2.9
-3
-50
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
40
-50
150
Figure 13. SS Charge Current vs Temperature
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 14. PWRGD Rdson vs Temperature
110
20
18
106
16
PWRGD - Leakage Current - nA
PWRGD Threshold - % Vref
Vsense (Fault) Rising
108
104
Vsense (Good) Falling
102
100
98
Vsense (Good) Falling
96
94
92
14
12
10
8
VIN = 5.5 V
6
4
Vsense (Fault) Falling
2
90
88
-50
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
0
-50
150
Figure 15. PWRGD Threshold vs Temperature
-25
0
25
50
75
100
TJ - Junction Temperature - °C
125
150
Figure 16. PWRGD Leakage Current vs Temperature
100
100
VO = 2.5 V
95
95
90
90
85
VO = 1.8 V
80
Efficiency - %
Efficiency - %
85
VO = 1.2 V
VO = 1 V
75
70
80
VO = 1.2 V
75
VO = 1 V
70
65
65
Vin = 3.3 V,
DCR = 6.8 mW,
Fs = 1 MHz,
Tj = 25°C
60
55
50
VO = 3.3 V
VO = 2.5 V
VO = 1.8 V
Vin = 5 V,
DCR = 6.8 mW,
Fs = 1 MHz,
Tj = 25°C
60
55
50
0
0.5
1
1.5
2
2.5
IO - Output Current - A
3
3.5
4
0
Figure 17. Efficiency vs Load Current
0.5
1
1.5
2
2.5
IO - Output Current - A
3
3.5
Figure 18. Efficiency vs Load Current
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
4
9
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Typical Characteristics (continued)
100
100
95
95
90
90
VO = 2.5 V
VO = 1.8 V
VO = 1.2 V
VO = 1 V
80
75
70
80
Vin = 3.3 V,
DCR = 18 mW,
Fs = 500 kHz,
Tj = 25°C
60
55
75
70
0
0.5
1
1.5
2
2.5
IO - Output Current - A
3
3.5
Vin = 5 V,
DCR = 18 mW,
Fs = 500 kHz,
Tj = 25°C
60
55
4
50
0
Figure 19. Efficiency vs Load Current
10
VO = 1.8 V
VO = 1.2 V
VO = 1 V
65
65
50
VO = 3.3 V
VO = 2.5 V
85
Efficiency - %
Efficiency - %
85
Submit Documentation Feedback
0.5
1
1.5
2
2.5
IO - Output Current - A
3
3.5
4
Figure 20. Efficiency vs Load Current
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
7 Detailed Description
7.1 Overview
The TPS54478 is a 6-V, 4-A, synchronous step-down (buck) converter with two integrated n-channel MOSFETs.
To improve performance during line and load transients the device implements a constant frequency, peak
current mode control which reduces output capacitance and simplifies external frequency compensation design.
The wide switching frequency of 200 kHz to 2000 kHz allows for efficiency and size optimization when selecting
the output filter components. The switching frequency is adjusted using a resistor to ground on the RT/CLK pin.
The device has an internal phase lock loop (PLL) on the RT/CLK pin that is used to synchronize the power
switch turn on to a falling edge of an external system clock.
The TPS54478 has a typical default start up voltage of 2.6 V. The EN pin has an internal pull-up current source
that can be used to adjust the input voltage under voltage lockout (UVLO) with two external resistors. In addition,
the pull up current provides a default condition when the EN pin is floating for the device to operate. The total
operating current for the TPS54478 is typically 525 μA when not switching and under no load. When the device
is disabled, the supply current is less than 2.5 μA.
The integrated 30 mΩ MOSFETs allow for high efficiency power supply designs with continuous output currents
up to 4 amperes.
The TPS54478 reduces the external component count by integrating the boot recharge diode. The bias voltage
for the integrated high side MOSFET is supplied by a capacitor between the BOOT and PH pins. The boot
capacitor voltage is monitored by an UVLO circuit and turns off the high side MOSFET when the voltage falls
below a preset threshold. This BOOT circuit allows the TPS54478 to operate approaching 100%. The output
voltage can be stepped down to as low as the 0.600 V reference.
TPS54478 features monotonic starup under pre-bias conditions. The low side Fet turns on for a very short time
period every cycle before the output voltage reaches the pre-biased voltage. This ensures the boot cap has
enough charge to turn on the top Fet when the output voltage reaches the pre-biased voltage.
The TPS54478 has a power good comparator (PWRGD) with 2% hysteresis.
The TPS54478 minimizes excessive output overvoltage transients by taking advantage of the overvoltage power
good comparator. When the regulated output voltage is greater than 107% of the nominal voltage, the
overvoltage comparator is activated, and the high side MOSFET is turned off and masked from turning on until
the output voltage is lower than 105%.
The SS/TR (slow start/tracking) pin is used to minimize inrush currents or provide power supply sequencing
during power up. A small value capacitor should be coupled to the pin for slow start. The SS/TR pin is
discharged before the output power up to ensure a repeatable restart after an overtemperature fault, UVLO fault
or disabled condition. To optimize the output startup waveform, two levels of SS current are implemented. The
first slope has more current so that the converter can get out of the region requiring small minimum ON time.
To reduce the power dissipation of TPS54478 during overcurrent event, the hiccup protection is implemented
beyond the cycle-by-cycle protection. Thermal shutdown prevents the overheat damage of the device.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
11
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
7.2 Functional Block Diagram
VIN
Shutdown
93%
Thermal
Shutdown
Enable
Comparator
Logic
Shutdown
Shutdown
Logic
107%
Enable
Threshold
Boot
Charge
Voltage
Reference
Boot
UVLO
Minimum
COMP Clamp
ERROR
AMPLIFIER
VSENSE
PWM
Comparator
SS/TR
Current
Sense
BOOT
PWM
Latch
Logic
R
Logic
S
Q
Shutdown
Logic
Slope
Compensation
PH
COMP
Overload
Recovery
Maximum
Clamp
Oscillator
with PLL
PGND
TPS54478RTE Block Diagram
GND
POWERPAD
RT/CLK
Copyright © 2016, Texas Instruments Incorporated
7.3 Feature Description
7.3.1 Fixed Frequency PWM Control
The TPS54478 uses an adjustable fixed frequency, peak current mode control. The output voltage is compared
through external resistors on the VSENSE pin to an internal voltage reference by an error amplifier which drives
the COMP pin. An internal oscillator initiates the turn on of the high side power switch. The error amplifier output
is compared to the high side power switch current. When the power switch current reaches the COMP voltage
level the high side power switch is turned off and the low side power switch is turned on. The COMP pin voltage
increases and decreases as the output current increases and decreases. The device implements a current limit
by clamping the COMP pin voltage to a maximum level and also implements a minimum clamp for improved
transient response performance.
7.3.2 Slope Compensation and Output Current
The TPS54478 adds a compensating ramp to the switch current signal. This slope compensation prevents subharmonic oscillations as duty cycle increases. The available peak inductor current remains constant over the full
duty cycle range.
12
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Feature Description (continued)
7.3.3 Bootstrap Voltage (BOOT) and Low Dropout Operation
The TPS54478 has an integrated boot regulator and requires a small ceramic capacitor between the BOOT and
PH pin to provide the gate drive voltage for the high side MOSFET. The value of the ceramic capacitor should be
0.1 μF. A ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10 V or higher is
recommended because of the stable characteristics over temperature and voltage.
To improve drop out, the TPS54478 is designed to operate at 100% duty cycle as long as the BOOT to PH pin
voltage is greater than 2.2 V. The high side MOSFET is turned off using an UVLO circuit, allowing for the low
side MOSFET to conduct when the voltage from BOOT to PH drops below 2.2 V. Since the supply current
sourced from the BOOT pin is very low, the high side MOSFET can remain on for more switching cycles than are
required to refresh the capacitor, thus the effective duty cycle of the switching regulator is very high.
7.3.4 Error Amplifier
The TPS54478 has a transconductance amplifier. The error amplifier compares the VSENSE voltage to the lower
of the SS/TR pin voltage or the internal 0.600 V voltage reference. The transconductance of the error amplifier is
225 μA/V during normal operation. When the voltage of VSENSE pin is below 0.600 V and the device is
regulating using the SS/TR voltage, the gm is typically greater than 77 μA/V, but less than 225 μA/V. The
frequency compensation components are placed between the COMP pin and ground.
7.3.5 Voltage Reference
The voltage reference system produces a precise ±1% voltage reference over temperature by scaling the output
of a temperature-stable bandgap circuit. The bandgap and scaling circuits produce 0.600 V at the non-inverting
input of the error amplifier.
7.3.6 Adjusting the Output Voltage
The output voltage is set with a resistor divider from the output node to the VSENSE pin. It is recommended to
use divider resistors with 1% tolerance or better. Start with a 20 kΩ for the R1 resistor and use the Equation 1 to
calculate R2. To improve efficiency at very light loads consider using larger value resistors. If the values are too
high the regulator is more susceptible to noise and voltage errors from the VSENSE input current are noticeable.
vertical spacer
vertical spacer
æ
ö
0.6 V
R2 = R1 ´ ç
÷
è VO - 0.6 V ø
(1)
TPS54478
VO
R1
VSENSE
–
R2
0.6 V
+
Copyright © 2016, Texas Instruments Incorporated
Figure 21. Voltage Divider Circuit
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
13
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Feature Description (continued)
7.3.7 Enable and Adjusting Undervoltage Lockout
The TPS54478 is disabled when the VIN pin voltage falls below 2.6 V. If an application requires a higher undervoltage lockout (UVLO), use the EN pin as shown in Figure 22 to adjust the input voltage UVLO by using two
external resistors. It is recommended to use the EN resistors to set the UVLO falling threshold (VSTOP) above 2.6
V. The rising threshold (VSTART) should be set to provide enough hysteresis to allow for any input supply
variations. The EN pin has an internal pull-up current source that provides the default condition of the TPS54478
operating when the EN pin floats. Once the EN pin voltage exceeds 1.30 V, an additional 2.76 μA of hysteresis is
added. When the EN pin is pulled below 1.21 V, the 2.76 μA is removed. This additional current facilitates input
voltage hysteresis.
TPS54478
i hys
VIN
2.76 mA
ip
R1
0.64 mA
R2
+
EN
Vena
–
Copyright © 2016, Texas Instruments Incorporated
Figure 22. Adjustable Undervoltage Lockout
æV
ö
VSTART ç ENFALLING ÷ - VSTOP
è VENRISING ø
R1 =
æ V
ö
Ip ç1 - ENFALLING ÷ + Ih
V
ENRISING ø
è
(2)
vertical spacer
R2 =
R1´ VENFALLING
VSTOP - VENFALLING + R1(Ip + Ih )
(3)
Where Ih = 2.76 µA, Ip = 0.64 µA, VENRISING = 1.30 V, VENFALLING = 1.21 V
7.3.8 Slow Start / Tracking Pin
The TPS54478 regulates to the lower of the SS/TR pin and the internal reference voltage. A capacitor on the
SS/TR pin to ground implements a slow start time. Before the SS pin reaches the voltage threshold VSSTHR, the
charge current is about 45 μA. The TPS54478 internal pull-up current source of 2.2 μA charges the external slow
start capacitor after the SS pin voltage exceeds VSSTHR. Equation 4 calculates the required slow start capacitor
value where Tss is the desired slow start time in ms and Css is the required capacitance in nF.
vertical spacer
Css(nF) = 3 ´ Tss(mS)
(4)
If during normal operation, the VIN goes below the UVLO, EN pin pulled below 1.21 V, or a thermal shutdown
event occurs, the TPS54478 stops switching. When the VIN goes above UVLO, EN is released or pulled high, or
a thermal shutdown is exited, then SS/TR is discharged to below 65 mV before reinitiating a powering up
sequence. The VSENSE voltage will follow the SS/TR pin voltage with a 65mV offset up to 90% of the internal
voltage reference. When the SS/TR voltage is greater than 90% of the internal reference voltage the offset
increases as the effective system reference transitions from the SS/TR voltage to the internal voltage reference.
14
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Feature Description (continued)
TPS54478
PWRGD1
EN1
EN2
EN1
EN1
SS1
SS2
Vo1
VO1
PWRGD2
PWRGD1
PWRGD1
Copyright © 2016, Texas Instruments Incorporated
Vo2
VO2
t - tTime
= 1 ms/div
= 1ms/div
Figure 23. Sequential Start-Up Sequence
Figure 24. Sequential Startup using EN and
PWRGD
TPS54478
EN1
EN1
SS/TR1
Io
Vo1
PWRGD1
Vo2
TPS54478
EN2
t - Time = 1 ms/div
SS/TR2
PWRGD2
Copyright © 2016, Texas Instruments Incorporated
Figure 25. Schematic for Ratio-metric Start-Up
Sequence
vertical spacer
Figure 26. Ratio-metric Startup
Simultaneous power supply sequencing can be implemented by connecting the resistor network of R1 and R2
shown in Figure 27 to the output of the power supply that needs to be tracked or another voltage reference
source. Using Equation 5 and Equation 6, the tracking resistors can be calculated. To minimize the effect of the
inherent SS/TR to VSENSE offset (Vssoffset) in the slow start circuit and the offset created by the pullup current
source (Iss) and tracking resistors, the Vssoffset and Iss are included as variables in the equations. As the
SS/TR voltage becomes more than 85% of the nominal reference voltage the Vssoffset becomes larger as the
slow start circuits gradually handoff the regulation reference to the internal voltage reference. The SS/TR pin
voltage needs to be greater than 0.86 V for a complete handoff to the internal voltage reference as shown in
Figure 28.
vertical spacer
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
15
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Feature Description (continued)
R1 =
Vout2
Vssoffset
´
Vref
Iss
(5)
vertical spacer
Vref ´ R1
R2 =
Vout2 - Vref
(6)
vertical spacer
vertical spacer
vertical spacer
TPS54478
EN1
VOUT1
SS/TR1
PWRGD1
TPS54478
EN2
VOUT 2
EN1 = 5 / div
SS2 = 500 mV / div
Vo1 = 500 mV / div
Vo2 = 500 mV / div
R1
SS/TR2
R2
PWRGD2
Time = 1 msec / div
Copyright © 2016, Texas Instruments Incorporated
Figure 27. Simultaneous Startup Sequence
Figure 28. Simultaneous Start-Up using Coupled
SS/TR Pins
7.3.9 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
The switching frequency of the TPS54478 is adjustable over a wide range from 200 kHz to 2000 kHz by placing
a maximum of 150 kΩ and minimum of 16 kΩ, respectively, on the RT/CLK pin. An internal amplifier holds this
pin at a fixed voltage when using an external resistor to ground to set the switching frequency. The RT/CLK is
typically 0.5 V. To determine the timing resistance for a given switching frequency, use the curve in Figure 5 or
Equation 7.
90066
RT (kW) =
Fs(kHz)1.135
(7)
vertical spacer
Fs(kHz) =
23439
RT(kW)0.8813
(8)
To reduce the solution size one would typically set the switching frequency as high as possible, but tradeoffs of
the efficiency, maximum input voltage and minimum controllable on time should be considered.
The minimum controllable on time is typically 100 ns at full current load and 120 ns at no load, and limits the
maximum operating input voltage or output voltage.
16
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Feature Description (continued)
7.3.10 Overcurrent Protection
The TPS54478 implements current mode control which uses the COMP pin voltage to turn off the high side
MOSFET and turn on the low side MOSFET on a cycle by cycle basis. Each cycle the switch current and the
COMP pin voltage are compared, when the peak switch current intersects the COMP voltage the high side
switch is turned off. During overcurrent conditions that pull the output voltage low, the error amplifier will respond
by driving the COMP pin high, increasing the switch current. The error amplifier output is clamped internally.
This clamp functions as a switch current limit. When the OCP reaches 512 cycles, the converter enters hiccup
mode in which no switching action happens for about 16000 cycles. This helps the reduction of the power
consumption during the over current event.
7.3.11 START-UP into Prebiased Output
The TPS54478 features monotonic startup into pre-biased output. The low side FET turns on for a very short
time period every cycle before the output voltage reaches the pre-biased voltage. This ensures the boot cap has
enough charge to turn on the top FET when the output voltage reaches the pre-biased voltage. The TPS54478
also implements low side current protection by detecting the voltage over the low side MOSFET. When the
converter sinks current through its low side FET is more than 3.1 A, the control circuit will turn the low side FET
off. Due to the implemented prebias function, the low side Fet reverse current protection should not be reached,
but it provides another layer of protection in the undesired events such as oscillation induced by load.
7.3.12 Synchronize Using the RT/CLK Pin
The RT/CLK pin is used to synchronize the converter to an external system clock. See Figure 29. To implement
the synchronization feature in a system, connect a square wave to the RT/CLK pin with an on time of at least
75ns. If the pin is pulled above the PLL upper threshold, a mode change occurs and the pin becomes a
synchronization input. The internal amplifier is disabled and the pin is a high impedance clock input to the
internal PLL. If clocking edges stop, the internal amplifier is re-enabled and the mode returns to the frequency set
by the resistor. The square wave amplitude at this pin must transition lower than 0.6 V and higher than 1.6 V
typically. The synchronization frequency range is 300 kHz to 2000 kHz. The rising edge of the PH is
synchronized to the falling edge of RT/CLK pin.
TPS54478
EXT_CLK
PLL
RT/CLK
Clock
Source
RT
Copyright © 2016, Texas Instruments Incorporated
PH
PH
t - Time = 1 ms/div
Figure 29. Synchronizing to a System Clock
Figure 30. Plot of Synchronizing to System Clock
7.3.13 Power Good (PWRGD Pin)
The PWRGD pin output is an open drain MOSFET. The output is pulled low when the VSENSE voltage enters
the fault condition by falling below 93% or rising above 107% of the nominal internal reference voltage. There is
a 2% hysteresis on the threshold voltage, so when the VSENSE voltage rises to the good condition above 95%
or falls below 105% of the internal voltage reference the PWRGD output MOSFET is turned off. It is
recommended to use a pull-up resistor between the values of 1 kΩ and 100 kΩ to a voltage source that is 6 V or
less. The PWRGD is in a valid state once the VIN input voltage is greater than 1.6 V.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
17
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Feature Description (continued)
7.3.14 Overvoltage Transient Protection
The TPS54478 incorporates an overvoltage transient protection (OVTP) circuit to minimize voltage overshoot
when recovering from output fault conditions or strong unload transients. The OVTP feature minimizes the output
overshoot by implementing a circuit to compare the VSENSE pin voltage to the OVTP threshold which is 107%
of the internal voltage reference. If the VSENSE pin voltage is greater than the OVTP threshold, the high side
MOSFET is disabled preventing current from flowing to the output and minimizing output overshoot. When the
VSENSE voltage drops lower than the OVTP threshold the high side MOSFET is allowed to turn on the next
clock cycle.
7.3.15 Thermal Shutdown
The device implements an internal thermal shutdown to protect itself if the junction temperature exceeds 165°C.
The thermal shutdown forces the device to stop switching when the junction temperature exceeds the thermal
trip threshold. Once the die temperature decreases below 150°C, the device reinitiates the power up sequence
by discharging the SS pin to below 65 mV. The thermal shutdown hysteresis is 15°C.
7.3.16 Small Signal Model for Loop Response
Figure 31 shows an equivalent model for the TPS54478 control loop which can be modeled in a circuit simulation
program to check frequency response and dynamic load response without slope compensation effect. The error
amplifier is a transconductance amplifier with a gm of 225 μA/V. The error amplifier can be modeled using an
ideal voltage controlled current source. The resistor R0 and capacitor Co model the open loop gain and
frequency response of the amplifier. The 1-mV AC voltage source between the nodes a and b effectively breaks
the control loop for the frequency response measurements. Plotting a/c shows the small signal response of the
frequency compensation. Plotting a/b shows the small signal response of the overall loop. The dynamic loop
response can be checked by replacing the RL with a current source with the appropriate load step amplitude and
step rate in a time domain analysis.
PH
VO
Power Stage
14 A/V
a
b
R1
c
R3
C2
RESR
RL
COMP
C1
CO RO
0.6 V
VSENSE
gm
225 µA/V
COUT
R2
Figure 31. Small Signal Model for Loop Response Without Slope Comp Effect
7.3.17 Simple Small Signal Model for Peak Current Mode Control
Figure 31 is a simple small signal model that can be used to understand how to design the frequency
compensation without slope compensation effect. The TPS54478 power stage can be approximated to a voltage
controlled current source (duty cycle modulator) supplying current to the output capacitor and load resistor. The
control to output transfer function is shown in Equation 9 and consists of a dc gain, one dominant pole and one
ESR zero. The quotient of the change in switch current and the change in COMP pin voltage (node c in
Figure 31) is the power stage transconductance. The gm for the TPS54478 is 14 A/V. The low frequency gain of
the power stage frequency response is the product of the transconductance and the load resistance as shown in
Equation 10. As the load current increases and decreases, the low frequency gain decreases and increases,
18
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Feature Description (continued)
respectively. This variation with load may seem problematic at first glance, but the dominant pole moves with
load current (see Equation 11). The combined effect is highlighted by the dashed line in the right half of
Figure 32. As the load current decreases, the gain increases and the pole frequency lowers, keeping the 0-dB
crossover frequency the same for the varying load conditions which makes it easier to design the frequency
compensation.
vertical spacer
vertical spacer
VO
Adc
VC
RESR
fp
RL
gmps
COUT
fz
Figure 32. Simple Small Signal Model and Frequency Response for Peak Current Mode Control without
Slope Comp Effect
æ
ç 1+
vo
è 2p
= Adc ´
vc
æ
ç 1+
è 2p
ö
s
÷
× ¦z ø
ö
s
÷
× ¦p ø
(9)
Adc = gmps ´ RL
¦p =
(10)
1
C OUT ´ R L ´ 2 p
(11)
vertical spacer
¦z =
COUT
1
´ RESR ´ 2p
(12)
7.3.18 Small Signal Model for Frequency Compensation
The TPS54478 uses a transconductance amplifier for the error amplifier and readily supports two of the
commonly used frequency compensation circuits. The compensation circuits are shown in Figure 33. The Type 2
circuits are most likely implemented in high bandwidth power supply designs using low ESR output capacitors. In
Type 2A, one additional high frequency pole is added to attenuate high frequency noise.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
19
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
Feature Description (continued)
VO
R1
VSENSE
COMP
gmea
R2
Vref
RO
CO
5pF
Type 2A
R3
C2
Type 2B
R3
C1
C1
Figure 33. Type-II of Frequency Compensation
The design guidelines for TPS54478 loop compensation are addressed in the Application Information section
with more details. The approach is to run the Pspice model first to find the accurate response of the power stage
with slope compensation effect. The compensation network is then designed based on the desired crossover
frequency. The crossover frequency and phase margin are more closer to the measured results when the slope
compensation effect is included.
For type-II compensation, the modulator pole, fpmod, and the esr zero, fz1 can be calculated using Equation 13
and Equation 14. Derating the output capacitor (COUT) is needed if the output voltage is a high percentage of the
capacitor rating. Use the capacitor manufacturer information to derate the capacitor value. Use Equation 15 and
Equation 16 to estimate a starting point for the crossover frequency, fc. Equation 15 is the geometric mean of the
modulator pole and the esr zero and Equation 16 is the mean of modulator pole and the switching frequency.
Use the lower value of Equation 15 or Equation 16 as the maximum crossover frequency.
¦ p m od =
Iout m ax
2 p ´ Vout ´ Cout
(13)
1
2 p ´ Resr ´ Cout
(14)
vertical spacer
¦ z m od =
vertical spacer
¦C =
¦p mod ´ ¦ z mod
(15)
vertical spacer
¦C =
¦p mod ´
¦ sw
2
(16)
vertical spacer
The type-III compensation is recommended to achieve higher crossover frequency by introducing extra phase lift.
By adding a small capacitor C3 in parallel with R1, one-pair of zero and pole is generated as given by
Equation 17 and Equation 18. The Application Information section provides step-by-step design guidelines for
Type-III compensation with the effect of slope compensation included.
20
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Feature Description (continued)
Vo
C3
R1
VSENSE
gm ea
R2
Vref
RO
COMP
CO
Type 3 A
R3
Type 3 B
R3
C2
5 pF
C1
C1
Figure 34. Type-III of Frequency Compensation
1
2p ´ R1´ C3
1
¦p =
2p ´ (R1/ /R2) ´ C3
¦z =
(17)
(18)
7.4 Device Functional Modes
7.4.1 PWM Operation
TPS54478 is a synchronous buck converter. Normal operation occurs when VIN is above 2.95 V and the SS/ENA
pins is high to enable the device.
7.4.2 Standby Operation
TPS54478 can be placed in standby when the SS/ENA pin is set low, disabling the device.
7.5 Programming
7.5.1 Sequencing
Many of the common power supply sequencing methods can be implemented using the SS/TR, EN, and
PWRGD pins. The sequential method can be implemented using an open drain or collector output of a power on
reset pin of another device. Figure 23 shows the sequential method. The PWRGD is coupled to the EN pin on
the TPS54478 which enables the second power supply once the primary supply reaches regulation.
Ratio-metric start up can be accomplished by connecting the SS/TR pins together. The regulator outputs ramp
up and reach regulation at the same time. When calculating the slow start time the pull up current source must
be doubled in Equation 4. The ratio metric method is illustrated in Figure 25.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
21
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
8 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.
8.1 Application Information
TPS54478 is a synchronous buck converter. It can convert an input voltage of 2.95 V to 6 V to a lower voltage.
Maximum output current is 4 A.
8.2 Typical Application
The schematic diagram for this design example is shown in Figure 36. The component reference designators of
this schematic are used for the equations in Detailed Design Procedure.
VIN
CBOOT
VIN
BOOT
CI
R4
TPS54478
EN
LO
VOUT
PH
CO
R5
R1
PWRGD
VSENSE
R2
SS/TR
RT /CLK
COMP
GND
AGND
POWERPAD
C ss
RT
R3
C1
Copyright © 2016, Texas Instruments Incorporated
Figure 35. Typical Application
8.2.1 Design Requirements
This example details the design of a high frequency switching regulator design using ceramic output capacitors.
This design is available as the TPS54478EVM-037 (PWR037) evaluation module (EVM). A few parameters must
be known in order to start the design process. These parameters are typically determined on the system level.
For this example, start with the following known parameters:
Table 1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Output Voltage
1.8 V
Transient Response 1 A to 3.0 A load step
ΔVout = 3%
Maximum Output Current
4A
Input Voltage
3 V to 6 V, 5 V nominal
Output Voltage Ripple
< 30 mV p-p
Switching Frequency (Fsw)
1000 kHz
22
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
8.2.2 Detailed Design Procedure
8.2.2.1 Selecting the Switching Frequency
The first step is to decide on a switching frequency for the regulator. Typically, choose the highest switching
frequency possible since this produces the smallest solution size. The high switching frequency allows for lower
valued inductors and smaller output capacitors compared to a power supply that switches at a lower frequency.
However, the highest switching frequency causes extra switching losses, which hurt the converter’s performance.
The converter is capable of running from 300 kHz to 2 MHz. Unless a small solution size is an ultimate goal, a
moderate switching frequency of 1 MHz is selected to achieve both a small solution size and a high efficiency
operation. Using Equation 7, R4 is calculated to be 35.4 kΩ. A standard 1% 35.7 kΩ value was chosen in the
design.
L1
1.2 mH
U1
TPS54478
VIN= 3-6 V
VIN
C1
C2
R1
10 mF
0.1 mF
14.3 kW
VSNS
C3
R2
220 pF
11.5 kW
C4
10
PH
11
C7
2 VIN
15 EN
6 VSNS
PH
12
0.1 mF
BOOT
13
PWRGD
14
9 SS/TR
GND
3
GND
4
AGND
5
C6
17
C5
820 pF
VOUT = 1.8 V, 4 A
2
35.7 kW
VOUT
R5
C8
C9
47 mF
47 mF
R6
20 kW
C10
220 pF
VIN
VSNS
100 kW
R7
PWPD
30.9 kW
R4
1
PH
7 COMP
8 RT/CLK
R3
1
16 VIN
1 VIN
10 kW
1
Optional
0.01 mF
Copyright © 2016, Texas Instruments Incorporated
Figure 36. High Frequency, 1.8 V Output Power Supply Design with Adjusted UVLO
8.2.2.2 Output Inductor Selection
The inductor selected works for the entire TPS54478 input voltage range. To calculate the value of the output
inductor, use Equation 19. KIND is a coefficient that represents the amount of inductor ripple current relative to the
maximum output current. The inductor ripple current is filtered by the output capacitor. Therefore, choosing high
inductor ripple currents impacts the selection of the output capacitor since the output capacitor must have a
ripple current rating equal to or greater than the inductor ripple current. In general, the inductor ripple value is at
the discretion of the designer; however, KIND is normally from 0.1 to 0.3 for the majority of applications.
For this design example, use KIND = 0.3 and the inductor value is calculated to be 1.05 μH. For this design, a
nearest standard value was chosen: 1.2 μH. For the output filter inductor, it is important that the RMS current and
saturation current ratings not be exceeded. The RMS and peak inductor current can be found from Equation 21
and Equation 22.
For this design, the RMS inductor current is 4.01 A and the peak inductor current is 4.53 A. The chosen inductor
is a Coilcraft XAL5030-122ME. It has a saturation current rating of 11.8 A (20% inductance loss) and a RMS
current rating of 8.7 A (20 °C temperature rise). The series resistance is 6.78 mΩ typical.
The current flowing through the inductor is the inductor ripple current plus the output current. During power up,
faults or transient load conditions, the inductor current can increase above the calculated peak inductor current
level calculated above. In transient conditions, the inductor current can increase up to the switch current limit of
the device. For this reason, the most conservative approach is to specify an inductor with a saturation current
rating equal to or greater than the switch current limit rather than the peak inductor current.
Vinmax - Vout
Vout
´
L1 =
Io ´ Kind
Vinmax ´ ¦ sw
(19)
vertical spacer
Iripple =
Vinmax - Vout
Vout
´
L1
Vinmax ´ ¦ sw
(20)
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
23
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
vertical spacer
Io 2 +
ILrms =
æ Vo ´ (Vinmax - Vo) ö
1
´ ç
÷
12
è Vinmax ´ L1 ´ ¦ sw ø
2
(21)
vertical spacer
ILpeak = Iout +
Iripple
2
(22)
8.2.2.3 Output Capacitor
There are three primary considerations for selecting the value of the output capacitor. The output capacitor
determines the modulator pole, the output voltage ripple, and how the regulator responds to a large change in
load current. The output capacitance needs to be selected based on the more stringent of these three criteria.
The desired response to a large change in the load current is the first criteria. The output capacitor needs to
supply the load with current when the regulator can not. This situation would occur if there are desired hold-up
times for the regulator where the output capacitor must hold the output voltage above a certain level for a
specified amount of time after the input power is removed. The regulator is temporarily not able to supply
sufficient output current if there is a large, fast increase in the current needs of the load such as transitioning
from no load to a full load. The regulator usually needs two or more clock cycles for the control loop to see the
change in load current and output voltage and adjust the duty cycle to react to the change. The output capacitor
must be sized to supply the extra current to the load until the control loop responds to the load change. The
output capacitance must be large enough to supply the difference in current for 2 clock cycles while only allowing
a tolerable amount of droop in the output voltage. Equation 23 shows the minimum output capacitance necessary
to accomplish this.
For this example, the transient load response is specified as a 3% change in Vout for a load step from 1 A (25%
load) to 3 A (75% load). For this example, ΔIout = 3 – 1 = 2.0 A and ΔVout = 0.03 × 1.8 = 0.054 V. Using these
numbers gives a minimum capacitance of 74.1 μF. This value does not take the ESR of the output capacitor into
account in the output voltage change. For ceramic capacitors, the ESR is usually small enough to ignore in this
calculation.
Equation 24 calculates the minimum output capacitance needed to meet the output voltage ripple specification.
Where fsw is the switching frequency, Vripple is the maximum allowable output voltage ripple, and Iripple is the
inductor ripple current. In this case, the maximum output voltage ripple is 30 mV. Under this requirement,
Equation 24 yields 4.4 uF.
vertical spacer
2 ´ DIout
Co >
¦ sw ´ DVout
where
•
ΔIout is the change in output current, fsw is the regulators switching frequency and ΔVout is the allowable
change in the output voltage.
(23)
vertical spacer
Co >
1
´
8 ´ ¦ sw
1
Voripple
Iripple
(24)
vertical spacer
Equation 25 calculates the maximum ESR an output capacitor can have to meet the output voltage ripple
specification. Equation 25 indicates the ESR should be less than 28.6 mΩ. In this case, the ESR of the ceramic
capacitor is much less than 28.6 mΩ.
Additional capacitance de-ratings for aging, temperature and DC bias should be factored in which increases this
minimum value. For this example, two 47 μF 10 V X5R ceramic capacitors with 3 mΩ of ESR are used. The
estimated capacitance after derating is 2 x 45 µF = 90 µF.
24
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
Capacitors generally have limits to the amount of ripple current they can handle without failing or producing
excess heat. An output capacitor that can support the inductor ripple current must be specified. Some capacitor
data sheets specify the RMS (Root Mean Square) value of the maximum ripple current. Equation 26 can be used
to calculate the RMS ripple current the output capacitor needs to support. For this application, Equation 26 yields
303 mA.
Voripple
Resr <
Iripple
(25)
vertical spacer
Icorm s =
Vout ´ (Vinm ax - Vout)
12 ´ Vinm ax ´ L1 ´ ¦ sw
(26)
8.2.2.4 Input Capacitor
The TPS54478 requires a high quality ceramic, type X5R or X7R, input decoupling capacitor of at least 10 μF of
effective capacitance and in some applications a bulk capacitance. The effective capacitance includes any DC
bias effects. The voltage rating of the input capacitor must be greater than the maximum input voltage. The
capacitor must also have a ripple current rating greater than the maximum input current ripple of the TPS54478.
The input ripple current can be calculated using Equation 27.
The value of a ceramic capacitor varies significantly over temperature and the amount of DC bias applied to the
capacitor. The capacitance variations due to temperature can be minimized by selecting a dielectric material that
is stable over temperature. X5R and X7R ceramic dielectrics are usually selected for power regulator capacitors
because they have a high capacitance to volume ratio and are fairly stable over temperature. The output
capacitor must also be selected with the DC bias taken into account. The capacitance value of a capacitor
decreases as the DC bias across a capacitor increases.
For this example design, a ceramic capacitor with at least a 10 V voltage rating is required to support the
maximum input voltage. For this example, one 10 μF and one 0.1 μF 10 V capacitors in parallel have been
selected. The input capacitance value determines the input ripple voltage of the regulator. The input voltage
ripple can be calculated using Equation 28. Using the design example values, Ioutmax = 4 A, Cin = 10 μF, Fsw =
1 MHz, yields an input voltage ripple of 99 mV and a rms input ripple current of 1.95 A.
Icirms = Iout ´
Vout
´
Vinmin
(Vinmin
- Vout )
Vinmin
(27)
vertical spacer
Ioutmax ´ 0.25
DVin =
Cin ´ ¦ sw
(28)
8.2.2.5 Slow Start Capacitor
The slow start capacitor determines the minimum amount of time it takes for the output voltage to reach its
nominal programmed value during power up. This is useful if a load requires a controlled voltage slew rate. This
is also used if the output capacitance is very large and would require large amounts of current to quickly charge
the capacitor to the output voltage level. The large currents necessary to charge the capacitor may make the
TPS54478 reach the current limit or excessive current draw from the input power supply may cause the input
voltage rail to sag. Limiting the output voltage slew rate solves both of these problems.
The slow start capacitor value can be calculated using Equation 29. For the example circuit, the slow start time is
not too critical since the output capacitor value is 2 x 47 μF which does not require much current to charge to 1.8
V. The example circuit has the slow start time set to an arbitrary value of 3.33 ms which requires a 10 nF
capacitor.
C6(nF) = 3 × Tss(mS)
(29)
8.2.2.6 Bootstrap Capacitor Selection
A 0.1-μF ceramic capacitor must be connected between the BOOT to PH pin for proper operation. It is
recommended to use a ceramic capacitor with X5R or better grade dielectric. The capacitor should have 10 V or
higher voltage rating.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
25
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
8.2.2.7 Output Voltage and Feedback Resistors Selection
For the example design, 10.0 kΩ was selected for R7. Using Equation 30, R6 is calculated as 20.0 kΩ. The
nearest standard 1% resistor is 20.0 kΩ.
æV
ö
R6 = R7 × ç OUT - 1÷
è VREF
ø
(30)
Due to the internal design of the TPS54478, there is a minimum output voltage limit for any given input voltage.
The output voltage can never be lower than the internal voltage reference of 0.6 V. Above 0.6 V, the output
voltage may be limited by the minimum controllable on time. The minimum output voltage in this case is given by
Equation 31:
Voutmin = Ontimemin ´ Fsmax ´ (Vinmax - loutmin ´ RDSmin ) - Ioutmin ´ (RL + RDSmin )
where
•
•
•
•
•
•
•
Voutmin = minimum achievable output voltage
Ontimemin = minimum controllable on-time (100 ns typical. 120 ns no load)
Fsmax = maximum switching frequency including tolerance
Vinmax = maximum input voltage
Ioutmin = minimum load current
RDSmin = minimum high-side MOSFET on resistance (see Electrical Characteristics)
RL = series resistance of output inductor
(31)
There is also a maximum achievable output voltage which is limited by the minimum off time. The maximum
output voltage is given by Equation 32:
æ Offtimemax ö
æ tdead ö
Voutmax = Vin ´ ç 1 ÷ - Ioutmax ´ (RDSmax + RI) - (0.7 - Ioutmax ´ RDSmax )´ ç ts ÷
ts
è
ø
è
ø
where
•
•
•
•
•
•
•
•
Voutmax = maximum achievable output voltage
Vin = minimum input voltage
Offtimemax = maximum off time (180 ns typical for adequate margin)
ts = 1/Fs
Ioutmax = maximum current
RDSmax = maximum high-side MOSFET on resistance (see Electrical Characteristics)
RI = DCR of the inductor
tdead = dead time (40 ns)
(32)
8.2.2.8 Compensation
There are several possible methods to design closed loop compensation for dc/dc converters. For the ideal
current mode control, the design equations can be easily simplified. The power stage gain is constant at low
frequencies, and rolls off at -20 dB/decade above the modulator pole frequency. The power stage phase is 0
degrees at low frequencies and starts to fall one decade above the modulator pole frequency reaching a
minimum of -90 degrees one decade above the modulator pole frequency. The modulator pole is a simple pole
shown in Equation 33.
1
FPMOD =
2 × p × COUT × ROUT
(33)
For the TPS54478 most circuits will have relatively high amounts of slope compensation. As more slope
compensation is applied, the power stage characteristics will deviate from the ideal approximations. The phase
loss of the power stage will now approach -180 degrees, making compensation more difficult. The power stage
transfer function can be solved but it is a tedious hand calculation that does not lend itself to simple
approximations. It is best to use Pspice or TINA-TI to accurately model the power stage gain and phase so that a
26
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
reliable compensation circuit can be designed. That is the technique used in this design procedure. Using the
pspice model of SLVM279 apply the values calculated previously to the output filter components of L1, C9, and
C10. Set Rload to the appropriate value. For this design, L1 = 1.2 µH. C8 and C9 use the derated capacitance
value of 45 µF, and the ESR is set to 3 mΩ. The Rload resistor is 1.8 / 4 = 450 mΩ. Now the power stage
characteristic can be plotted as shown in Figure 37.
60
180
40
120
Gain - dB
60
-0
0
-12.03 dB
-20
Phase
-60
-120
-40
-60
0.1
Phase - Degrees
Gain
20
>>
1
10
100
-180
1000
Frequency - kHz
Figure 37. Power Stage Gain and Phase Characteristics
For this design, the intended crossover frequency is 70 kHz. From the power stage gain and phase plots, the
gain at 70 kHz is -12.03 dB and the phase is -131.86 degrees. For 60 degrees of phase margin, additional phase
boost from a feed forward capacitor in parallel with the upper resistor of the voltage set point divider will be
required. R3 sets the gain of the compensated error amplifier to be equal and opposite the power stage gain at
crossover. The required value of R3 can be calculated from Equation 34.
R3 =
-GPWRSTG
10 20
gmEA
×
Vout
VREF
(34)
To maximize phase gain, the compensator zero is placed one decade below the crossover frequency of 70 kHz.
The required value for C5 is given by Equation 35.
1
C5 =
F
2 × p × R3 × CO
10
(35)
To maximize phase gain the high frequency pole is not implemented and C4 is not populated. The pole can be
useful to offset the ESR of aluminum electrolytic output capacitors. If desired the value for C4 can be calculated
from Equation 36.
1
C4 =
2 × p × R3 × FP
(36)
For maximum phase boost, the pole frequency FP will typically be one decade above the intended crossover
frequency FCO.
The feed forward capacitor C10, is used to increase the phase boost at crossover above what is normally
available from Type II compensation. It places an additional zero/pole pair located at Equation 37 and
Equation 38.
1
FZ =
2 × p × C10 × R6
(37)
1
FP =
2 × p × C10 × R6 P R7
(38)
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
27
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
This zero and pole pair is not independent. Once the zero location is chosen, the pole is fixed as well. For
optimum performance, the zero and pole should be located symmetrically about the intended crossover
frequency. The required value for C10 can calculated from Equation 39.
1
C10 =
VREF
2 × p × R6 × FCO ×
VOUT
(39)
For this design the calculated values for the compensation components are R3 = 30.6 kΩ ,C5 = 736 pF and C10
= 197 pF. Using standard values, the compensation components are R3 = 30.9 kΩ ,C5 = 820 pF and C10 = 220
pF.
8.2.3 Application Curves
100
100
90
90
VIN = 3.3 V
80
60
50
40
60
VIN = 5 V
50
40
30
30
20
20
10
10
0
0
0.5
VIN = 3.3 V
70
Efficiency - %
Efficiency - %
80
VIN = 5 V
70
1
1.5
2
2.5
Output Current - A
3
3.5
4
0
0.001
Figure 38. Efficiency vs Load Current
0.01
0.1
Output Current - A
1
10
Figure 39. Efficiency vs Load Current
VIN = 5 V/div
VOUT = 50 mV / div (ac coupled)
EN = 5 V/div
VOUT = 2 V/div
IOUT = 1 A / div
Load step = 1 - 3 A, slew rate = 0.167 A / ms
PWRGD = 5 V/div
Time = 100 ms/div
Figure 40. Transient Response, 2 A Step
28
Submit Documentation Feedback
Time = 2 ms/div
Figure 41. Power Up VOUT, VIN
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
VIN = 5 V/div
EN = 5 V/div
EN = 5 V/div
VOUT = 2 V/div
VOUT = 500 mV/div
PWRGD = 5 V/div
Pre-bias voltage = 500 mV
Time = 2 ms/div
Figure 42. Power Up VOUT, EN
Time = 2 msec / div
Figure 43. Power Up into Prebias Voltage
VIN = 5 V/div
VIN = 5 V/div
EN = 5 V/div
EN = 5 V/div
VOUT = 2 V/div
VOUT = 2 V/div
PWRGD = 5 V/div
PWRGD = 5 V/div
Time = 2 ms/div
Figure 45. Power Down VOUT, EN
Time = 2 ms/div
Figure 44. Power Down VOUT, VIN
VIN = 100 mV/div (ac coupled)
VOUT = 20 mV/div (ac coupled)
PH = 2 V/div
PH = 2 V/div
Time = 500 ns/div
Figure 46. Output Ripple, IOUT = 4 A
Time = 500 ns/div
Figure 47. Input Ripple, IOUT = 4 A
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
29
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
60
180
50
150
0.2
0.15
120
40
VIN = 5 V
Gain - dB
20
60
Gain
10
30
0
0
Phase - Degrees
90
30
Output Voltage Deviation - %
Phase
0.1
0.05
VIN = 3.3 V
0
-10
-30
-20
-60
-30
-90
-40
-120
-50
-150
-0.15
-180
-0.2
-60
10
100
1k
10k
f - Frequency - Hz
100k
1M
-0.05
-0.1
0
Figure 48. Closed Loop Response, VIN = 5 V, IOUT = 4 A
0.5
1
1.5
2
2.5
Output Current - A
3
3.5
4
Figure 49. Output Voltage Regulation vs Load Current
0.1
IOUT = 2 A
0.08
VOUT = 1 V/div
Output Voltage Deviation - %
0.06
0.04
0.02
0
-0.02
-0.04
IOUT = 5 A/div
-0.06
-0.08
-0.1
3
3.5
4
4.5
Input Voltage - V
5
5.5
6
Time = 1 ms/div
Figure 51. Hiccup Mode Current Limit
Figure 50. Output Voltage Regulation vs Input Voltage
VOUT = 1 V/div
VOUT = 500 mV/div
IOUT = 5 A/div
Time = 5 ms/div
Figure 52. Hiccup Mode Current Limit
Time = 500 ms/div
Figure 53. Start Up Characteristic
9 Power Supply Recommendations
The device is designed to operate from an input-voltage supply range between 2.95 V and 6 V. This input supply
should be well regulated. If the input supply is located more than a few inches from the converter, additional bulk
capacitance may be required in addition to the ceramic bypass capacitors. An electrolytic capacitor with a value
of 100 μF is a typical choice.
30
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
10 Layout
10.1 Layout Guidelines
Layout is a critical portion of good power supply design. There are several signal paths that conduct fast
changing currents or voltages that can interact with stray inductance or parasitic capacitance to generate noise
or degrade the power supplies performance. Care should be taken to minimize the loop area formed by the
bypass capacitor connections and the VIN pins. See Figure 54 for a PCB layout example. The GND pins and
AGND pin should be tied directly to the power pad under the IC. The power pad should be connected to any
internal PCB ground planes using multiple vias directly under the IC. Additional vias can be used to connect the
top side ground area to the internal planes near the input and output capacitors. For operation at full rated load,
the top side ground area along with any additional internal ground planes must provide adequate heat dissipating
area.
Locate the input bypass capacitor as close to the IC as possible. The PH pin should be routed to the output
inductor. Since the PH connection is the switching node, the output inductor should be located very close to the
PH pins, and the area of the PCB conductor minimized to prevent excessive capacitive coupling. The boot
capacitor must also be located close to the device. The sensitive analog ground connections for the feedback
voltage divider, compensation components, slow start capacitor and frequency set resistor should be connected
to a separate analog ground trace as shown. The RT/CLK pin is particularly sensitive to noise so the RT resistor
should be located as close as possible to the IC and routed with minimal lengths of trace. The additional external
components can be placed approximately as shown. It may be possible to obtain acceptable performance with
alternate PCB layouts, however this layout has been shown to produce good results and is meant as a guideline.
10.2 Layout Example
VIA to
Ground
Plane
UVLO SET
RESISTORS
VIN
INPUT
BYPASS
CAPACITOR
BOOT
PWRGD
EN
VIN
VIN
BOOT
CAPACITOR
VIN
OUTPUT
INDUCTOR
PH
VIN
PH
EXPOSED
POWERPAD
AREA
GND
PH
GND
PH
VOUT
OUTPUT
FILTER
CAPACITOR
SLOW START
CAPACITOR
RT/CLK
COMP
VSENSE
AGND
SS
FEEDBACK
RESISTORS
ANALOG
GROUND
TRACE
FREQUENCY
SET
RESISTOR
COMPENSATION
NETWORK
TOPSIDE
GROUND
AREA
VIA to Ground Plane
Figure 54. PCB Layout Example
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
31
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
10.3 Power Dissipation Estimate
The following formulas show how to estimate the IC power dissipation under continuous conduction mode (CCM)
operation. The power dissipation of the IC (Ptot) includes conduction loss (Pcon), dead time loss (Pd), switching
loss (Psw), gate drive loss (Pgd) and supply current loss (Pq).
Pcon = Io2 × RDS_on_Temp
Pd = ƒsw × Io × 0.7 × 40 × 10–9
Psw = 1/2 × Vin × Io × ƒsw× 7 × 10–9
Pgd = 2 × Vin × ƒsw× 6 × 10–9
Pq = Vin × 525 × 10–6
Where:
IO is the output current (A).
RDS_on_Temp is the on-resistance of the high-side MOSFET with given temperature (Ω).
Vin is the input voltage (V).
ƒsw is the switching frequency (Hz).
So
Ptot = Pcon + Pd + Psw + Pgd + Pq
For given TA,
TJ = TA + Rth × Ptot
For given TJMAX = 150°C
TAmax = TJmax – Rth × Ptot
Where:
Ptot is the total device power dissipation (W).
TA is the ambient temperature (°C).
TJ is the junction temperature (°C).
Rth is the thermal resistance of the package (°C/W).
TJMAX is maximum junction temperature (°C).
TAMAX is maximum ambient temperature (°C).
There are additional power losses in the regulator circuit due to the inductor AC and DC losses and trace
resistance that impact the overall efficiency of the regulator.
32
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
TPS54478
www.ti.com
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.1.2 Custom Design With WEBENCH® Tools
Click here to create a custom design using the TPS54478 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
• Run electrical simulations to see important waveforms and circuit performance
• Run thermal simulations to understand board thermal performance
• Export customized schematic and layout into popular CAD formats
• Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
11.2 Documentation Support
11.2.1 Related Documentation
For related documentation see the following:
• For SWIFT™ documentation, see the TI website at www.ti.com/swift
• TPS54478EVM-037 4-A, SWIFT™ Regulator Evaluation Module User's Guide (SLVU470)
11.3 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.
11.4 Community Resources
The following links connect to TI community resources. Linked contents are 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.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.5 Trademarks
SWIFT, E2E are trademarks of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
33
TPS54478
SLVSAS2B – JUNE 2011 – REVISED APRIL 2018
www.ti.com
11.6 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.
11.7 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 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
Submit Documentation Feedback
Copyright © 2011–2018, Texas Instruments Incorporated
Product Folder Links: TPS54478
PACKAGE OPTION ADDENDUM
www.ti.com
8-Apr-2018
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)
TPS54478RTER
ACTIVE
WQFN
RTE
16
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 150
54478
TPS54478RTET
ACTIVE
WQFN
RTE
16
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 150
54478
(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 OPTION ADDENDUM
www.ti.com
8-Apr-2018
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
30-Apr-2018
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
TPS54478RTER
WQFN
RTE
16
3000
330.0
12.4
3.3
3.3
1.1
8.0
12.0
Q2
TPS54478RTET
WQFN
RTE
16
250
180.0
12.4
3.3
3.3
1.1
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
30-Apr-2018
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
TPS54478RTER
WQFN
RTE
16
3000
367.0
367.0
35.0
TPS54478RTET
WQFN
RTE
16
250
210.0
185.0
35.0
Pack Materials-Page 2
IMPORTANT NOTICE
Texas Instruments Incorporated (TI) reserves the right to make corrections, enhancements, improvements and other changes to its
semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers
should obtain the latest relevant information before placing orders and should verify that such information is current and complete.
TI’s published terms of sale for semiconductor products (http://www.ti.com/sc/docs/stdterms.htm) apply to the sale of packaged integrated
circuit products that TI has qualified and released to market. Additional terms may apply to the use or sale of other types of TI products and
services.
Reproduction of significant portions of TI information in TI data sheets is permissible only if reproduction is without alteration and is
accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such reproduced
documentation. Information of third parties may be subject to additional restrictions. Resale of TI products or services with statements
different from or beyond the parameters stated by TI for that product or service voids all express and any implied warranties for the
associated TI product or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements.
Buyers and others who are developing systems that incorporate TI products (collectively, “Designers”) understand and agree that Designers
remain responsible for using their independent analysis, evaluation and judgment in designing their applications and that Designers have
full and exclusive responsibility to assure the safety of Designers' applications and compliance of their applications (and of all TI products
used in or for Designers’ applications) with all applicable regulations, laws and other applicable requirements. Designer represents that, with
respect to their applications, Designer has all the necessary expertise to create and implement safeguards that (1) anticipate dangerous
consequences of failures, (2) monitor failures and their consequences, and (3) lessen the likelihood of failures that might cause harm and
take appropriate actions. Designer agrees that prior to using or distributing any applications that include TI products, Designer will
thoroughly test such applications and the functionality of such TI products as used in such applications.
TI’s provision of technical, application or other design advice, quality characterization, reliability data or other services or information,
including, but not limited to, reference designs and materials relating to evaluation modules, (collectively, “TI Resources”) are intended to
assist designers who are developing applications that incorporate TI products; by downloading, accessing or using TI Resources in any
way, Designer (individually or, if Designer is acting on behalf of a company, Designer’s company) agrees to use any particular TI Resource
solely for this purpose and subject to the terms of this Notice.
TI’s provision of TI Resources does not expand or otherwise alter TI’s applicable published warranties or warranty disclaimers for TI
products, and no additional obligations or liabilities arise from TI providing such TI Resources. TI reserves the right to make corrections,
enhancements, improvements and other changes to its TI Resources. TI has not conducted any testing other than that specifically
described in the published documentation for a particular TI Resource.
Designer is authorized to use, copy and modify any individual TI Resource only in connection with the development of applications that
include the TI product(s) identified in such TI Resource. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE
TO ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY TECHNOLOGY OR INTELLECTUAL PROPERTY
RIGHT OF TI OR ANY THIRD PARTY IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
regarding or referencing third-party products or services does not constitute a license to use such products or services, or a warranty or
endorsement thereof. Use of TI Resources may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
TI RESOURCES ARE PROVIDED “AS IS” AND WITH ALL FAULTS. TI DISCLAIMS ALL OTHER WARRANTIES OR
REPRESENTATIONS, EXPRESS OR IMPLIED, REGARDING RESOURCES OR USE THEREOF, INCLUDING BUT NOT LIMITED TO
ACCURACY OR COMPLETENESS, TITLE, ANY EPIDEMIC FAILURE WARRANTY AND ANY IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF ANY THIRD PARTY INTELLECTUAL
PROPERTY RIGHTS. TI SHALL NOT BE LIABLE FOR AND SHALL NOT DEFEND OR INDEMNIFY DESIGNER AGAINST ANY CLAIM,
INCLUDING BUT NOT LIMITED TO ANY INFRINGEMENT CLAIM THAT RELATES TO OR IS BASED ON ANY COMBINATION OF
PRODUCTS EVEN IF DESCRIBED IN TI RESOURCES OR OTHERWISE. IN NO EVENT SHALL TI BE LIABLE FOR ANY ACTUAL,
DIRECT, SPECIAL, COLLATERAL, INDIRECT, PUNITIVE, INCIDENTAL, CONSEQUENTIAL OR EXEMPLARY DAMAGES IN
CONNECTION WITH OR ARISING OUT OF TI RESOURCES OR USE THEREOF, AND REGARDLESS OF WHETHER TI HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
Unless TI has explicitly designated an individual product as meeting the requirements of a particular industry standard (e.g., ISO/TS 16949
and ISO 26262), TI is not responsible for any failure to meet such industry standard requirements.
Where TI specifically promotes products as facilitating functional safety or as compliant with industry functional safety standards, such
products are intended to help enable customers to design and create their own applications that meet applicable functional safety standards
and requirements. Using products in an application does not by itself establish any safety features in the application. Designers must
ensure compliance with safety-related requirements and standards applicable to their applications. Designer may not use any TI products in
life-critical medical equipment unless authorized officers of the parties have executed a special contract specifically governing such use.
Life-critical medical equipment is medical equipment where failure of such equipment would cause serious bodily injury or death (e.g., life
support, pacemakers, defibrillators, heart pumps, neurostimulators, and implantables). Such equipment includes, without limitation, all
medical devices identified by the U.S. Food and Drug Administration as Class III devices and equivalent classifications outside the U.S.
TI may expressly designate certain products as completing a particular qualification (e.g., Q100, Military Grade, or Enhanced Product).
Designers agree that it has the necessary expertise to select the product with the appropriate qualification designation for their applications
and that proper product selection is at Designers’ own risk. Designers are solely responsible for compliance with all legal and regulatory
requirements in connection with such selection.
Designer will fully indemnify TI and its representatives against any damages, costs, losses, and/or liabilities arising out of Designer’s noncompliance with the terms and provisions of this Notice.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2018, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertising