7
8
9
10
24
23
22
21
VO1
PGOOD
VBST1
DRVH1
VO2
VREG3
VBST2
DRVH2
TPS51125RGE
11
12
20
19
LL1
DRVL1
LL2
DRVL2
13 14 15 16 17 18
EN0
SKIPSEL
GND
VIN
VREG5
VCLK
6 5 4 3 2 1
ENTRIP2
VFB2
TONSEL
VREF
VFB1
ENTRIP1
PowerPAD
220 nF
20 kW20 kW30 kW
100 kW
VREG5
33 mF
5.1 W
0.1 mF
130 kW130 kW
3.3 mF
330 mF
VO1
5 V
VIN
VREG5
VIN
10 mF x 2
VIN
5.5 V
to
28 V
EN0
5.1 W
0.1 mF
3.3 mF
330 mF
VO2
3.3 V
10 mF x 2
10 mF
13 kW
UDG-09019
VIN
100 nF 1 mF
15 V
100 nF
100 nF
100 nF
620 kW
VO1VREF
TPS51125
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SLUS786G –OCTOBER 2007–REVISED JUNE 2012
Dual-Synchronous, Step-Down Controller with Out-of-Audio™ Operation
and 100-mA LDOs for Notebook System Power
Check for Samples: TPS51125
1FEATURES APPLICATIONS
2• Wide Input Voltage Range: 5.5 V to 28 V • Notebook Computers
• Output Voltage Range: 2 V to 5.5 V • I/O Supplies
• Built-in 100-mA 5-V/3.3-V LDO with Switches • System Power Supplies
• Built-in 1% 2-V Reference Output DESCRIPTION
• With/Without Out-of-Audio™ Mode Selectable The TPS51125 is a cost effective, dual-synchronous
Light Load and PWM only Operation buck controller targeted for notebook system power
• Internal 1.6-ms Voltage Servo Softstart supply solutions. It provides 5-V and 3.3-V LDOs and
• Adaptive On-Time Control Architecture with requires few external components. The 270-kHz
VCLK output can be used to drive an external charge
Four Selectable Frequency Setting pump, generating gate drive voltage for the load
• 4500 ppm/°C RDS(on) Current Sensing switches without reducing the main converter’s
• Built-In Output Discharge efficiency. The TPS51125 supports high efficiency,
• Power Good Output fast transient response and provides a combined
power-good signal. Out-of-Audio™ mode light-load
• Built-in OVP/UVP/OCP operation enables low acoustic noise at much higher
• Thermal Shutdown (Non-latch) efficiency than conventional forced PWM operation.
• QFN, 24-Pin (RGE) Adaptive on-time D-CAP™ control provides
convenient and efficient operation. The part operates
with supply input voltages ranging from 5.5 V to 28 V
and supports output voltages from 2 V to 5.5 V. The
TPS51125 is available in a 24-pin QFN package and
is specified from -40°C to 85°C ambient temperature
range.
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2Out-of-Audio, D-CAP are trademarks of Texas Instruments.
PRODUCTION DATA information is current as of publication date. Copyright © 2007–2012, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
ORDERING INFORMATION
ORDERABLE OUTPUT MINIMUM
TAPACKAGE PINS ECO PLAN
DEVICE NUMBER SUPPLY QUANTITY
TPS51125RGET Tape-and-Reel 250
Plastic Quad Flat
-40°C to 85°C 24 Green (RoHS and no Sb/Br)
Pack (QFN) TPS51125RGER Tape-and-Reel 3000
ABSOLUTE MAXIMUM RATINGS(1)
over operating free-air temperature range (unless otherwise noted) VALUE
PARAMETER UNIT
MIN MAX
VBST1, VBST2 –0.3 36
VIN –0.3 30
LL1, LL2 –2.0 30
Input voltage range (1) LL1, LL2, pulse width < 20 ns –5.0 30
VBST1, VBST2 (2) –0.3 6 V
EN0, ENTRIP1, ENTRIP2, VFB1, VFB2, VO1, VO2, TONSEL, –0.3 6
SKIPSEL
DRVH1, DRVH2 –1.0 36
Output voltage range (1) DRVH1, DRVH2 (2) –0.3 6
PGOOD, VCLK, VREG3, VREG5, VREF, DRVL1, DRVL2 –0.3 6
Human Body Model QSS 009-105 (JESD22-A114A) 2
Electrostatic discharge kV
Charged Device Model QSS 009-147 (JESD22-C101B.01) 1.5
Junction temperature range, TJ–40 125 °C
Storage temperature, Tstg –55 150
(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 "recommended operating
conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) Voltage values are with respect to the corresponding LLx terminal.
DISSIPATION RATINGS
2-oz. trace and copper pad with solder. DERATING FACTOR ABOVE TA
PACKAGE TA< 25°C POWER RATING TA= 85°C POWER RATING
= 25°C
24 pin RGE(1) 1.85 W 18.5 mW/°C 0.74 W
(1) Enhanced thermal conductance by 3x3 thermal vias beneath thermal pad.
RECOMMENDED OPERATING CONDITIONS
over operating free-air temperature range (unless otherwise noted)
PARAMETER MIN TYP MAX UNIT
Supply voltage VIN 5.5 28
VBST1, VBST2 –0.1 34
VBST1, VBST2 (wrt LLx) –0.1 5.5
Input voltage range EN0, ENTRIP1, ENTRIP2, VFB1, VFB2, VO1, VO2, TONSEL, –0.1 5.5
SKIPSEL V
DRVH1, DRVH2 –0.8 34
DRVH1, DRVH2 (wrt LLx) –0.1 5.5
Output voltage range LL1, LL2 –1.8 28
VREF, VREG3, VREG5 –0.1 5.5
PGOOD, VCLK, DRVL1, DRVL2 –0.1 5.5
Operating free-air temperature –40 85 °C
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ELECTRICAL CHARACTERISTICS
over operating free-air temperature range, VIN = 12 V (unless otherwise noted)
PARAMETER CONDITIONS MIN TYP MAX UNIT
SUPPLY CURRENT
VIN current, T A= 25°C, no load, VO1 = 0 V, VO2
IVIN1 VIN supply current1 = 0 V, EN0=open, ENTRIPx = 5 V, 0.55 1 mA
VFB1 = VFB2 = 2.05 V
VIN current, TA= 25°C, no load, VO1 = 5 V, VO2 =
IVIN2 VIN supply current2 3.3 V, EN0=open, ENTRIPx = 5 V, 4 6.5 μA
VFB1 = VFB2 = 2.05 V
VO1 current, TA= 25°C, no load, VO1 = 5 V, VO2
IVO1 VO1 current = 3.3 V, EN0=open, ENTRIPx = 5 V, 0.8 1.5 mA
VFB1 = VFB2 = 2.05 V
VO2 current, TA= 25°C, no load, VO1 = 5 V, VO2
IVO2 VO2 current = 3.3 V, EN0=open, ENTRIPx = 5 V, 12 100
VFB1 = VFB2 = 2.05 V
VIN current, TA= 25°C, no load, μA
IVINSTBY VIN standby current 95 250
EN0 = 1.2 V, ENTRIPx = 0 V
VIN current, TA= 25°C, no load,
IVINSDN VIN shutdown current 10 25
EN0 = ENTRIPx = 0 V
VREF OUTPUT
IVREF = 0 A 1.98 2.00 2.02
VVREF VREF output voltage V
-5 μA < IVREF < 100 μA 1.97 2.00 2.03
VREG5 OUTPUT
VO1 = 0 V, IVREG5 < 100 mA, TA= 25°C 4.8 5 5.2
VVREG5 VREG5 output voltage VO1 = 0 V, IVREG5 < 100 mA, 6.5 V < VIN < 28 V 4.75 5 5.25 V
VO1 = 0 V, IVREG5 < 50 mA, 5.5 V < VIN < 28 V 4. 75 5 5.25
IVREG5 VREG5 output current VO1 = 0 V, VREG5 = 4.5 V 100 175 250 mA
Turns on 4.55 4.7 4.85
VTH5VSW Switch over threshold V
Hysteresis 0.15 0.25 0.3
R5VSW 5 V SW RON VO1 = 5 V, IVREG5 = 100 mA 1 3 Ω
VREG3 OUTPUT
VO2 = 0 V, IVREG3 < 100 mA, TA= 25°C 3.2 3.33 3.46
VVREG3 VREG3 output voltage VO2 = 0 V, IVREG3 < 100 mA, 6.5 V < VIN < 28 V 3.13 3.33 3.5 V
VO2 = 0 V, IVREG3 < 50 mA, 5.5 V < VIN < 28 V 3.13 3.33 3.5
IVREG3 VREG3 output current VO2 = 0 V, VREG3 = 3 V 100 175 250 mA
Turns on 3.05 3.15 3.25
VTH3VSW Switch over threshold V
Hysteresis 0.1 0.2 0.25
R3VSW 3 V SW RON VO2 = 3.3 V, IVREG3 = 100 mA 1.5 4 Ω
INTERNAL REFERENCE VOLTAGE
VIREF Internal reference voltage IVREF = 0 A, beginning of ON state 1.95 1.98 2.01
FB voltage, IVREF = 0 A, skip mode 1.98 2.01 2.04 V
VVFB VFB regulation voltage FB voltage, IVREF = 0 A, OOA mode (1) 2.00 2.035 2.07
FB voltage, IVREF = 0 A, continuous conduction (1) 2.00
IVFB VFB input current VFBx = 2.0 V, TA= 25°C -20 20 nA
(1) Ensured by design. Not production tested.
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ELECTRICAL CHARACTERISTICS (continued)
over operating free-air temperature range, VIN = 12 V (unless otherwise noted)
PARAMETER CONDITIONS MIN TYP MAX UNIT
VOUT DISCHARGE
IDischg VOUT discharge current ENTRIPx = 0 V, VOx = 0.5 V 10 60 mA
OUTPUT DRIVERS
Source, VBSTx - DRVHx = 100 mV 4 8
RDRVH DRVH resistance Sink, VDRVHx - LLx = 100 mV 1.5 4 Ω
Source, VVREG5 - DRVLx = 100 mV 4 8
RDRVL DRVL resistance Sink, VDRVLx = 100 mV 1.5 4
DRVHx-off to DRVLx-on 10
tDDead time ns
DRVLx-off to DRVHx-on 30
CLOCK OUTPUT
VCLKH High level voltage IVCLK = -10 mA, VO1 = 5 V, TA= 25 °C 4.84 4.92 V
VCLKL Low level voltage IVCLK = 10 mA, VO1 = 5 V, TA= 25 °C 0.06 0.12
fCLK Clock frequency TA= 25 °C 175 270 325 kHz
INTERNAL BST DIODE
VFBST Forward voltage VVREG5-VBSTx, IF= 10 mA, TA= 25 °C 0.7 0.8 0.9 V
IVBSTLK VBST leakage current VBSTx = 34 V, LLx = 28 V, TA= 25 °C 0.1 1 μA
DUTY AND FREQUENCY CONTROL
tON11 CH1 on time 1 VIN = 12 V, VO1 = 5 V, 200 kHz setting 2080
tON12 CH1 on time 2 VIN = 12 V, VO1 = 5 V, 245 kHz setting 1700
tON13 CH1 on time 3 VIN = 12 V, VO1 = 5 V, 300 kHz setting 1390
tON14 CH1 on time 4 VIN = 12 V, VO1 = 5 V, 365 kHz setting 1140
tON21 CH2 on time 1 VIN = 12 V, VO2 = 3.3 V, 250 kHz setting 1100 ns
tON22 CH2 on time 2 VIN = 12 V, VO2 = 3.3 V, 305 kHz setting 900
tON23 CH2 on time 3 VIN = 12 V, VO2 = 3.3 V, 375 kHz setting 730
tON24 CH2 on time 4 VIN = 12 V, VO2 = 3.3 V, 460 kHz setting 600
tON(min) Minimum on time TA= 25 °C 80
tOFF(min) Minimum off time TA= 25 °C 300
SOFT START
tSS Internal SS time Internal soft start 1.1 1.6 2.1 ms
POWERGOOD
PG in from lower 92.50% 95% 97.50%
102.50 107.50
VTHPG PG threshold PG in from higher 105%
% %
PG hysteresis 2.50% 5% 7.50%
IPGMAX PG sink current PGOOD = 0.5 V 5 12 mA
tPGDEL PG delay Delay for PG in 350 510 670 μs
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SLUS786G –OCTOBER 2007–REVISED JUNE 2012
ELECTRICAL CHARACTERISTICS (continued)
over operating free-air temperature range, VIN = 12 V (unless otherwise noted)
PARAMETER CONDITIONS MIN TYP MAX UNIT
LOGIC THRESHOLD AND SETTING CONDITIONS
Shutdown 0.4
VEN0 EN0 setting voltage Enable, VCLK = off 0.8 1.6 V
Enable, VCLK = on 2.4
VEN0 = 0.2 V 2 3.5 5
IEN0 EN0 current μA
VEN0 = 1.5 V 1 1.75 2.5
Shutdown 350 400 450
ENTRIP1, ENTRIP2
VEN mV
threshold Hysteresis 10 30 60
200 kHz/250 kHz 1.5
245 kHz/305 kHz 1.9 2.1
VTONSEL TONSEL setting voltage 300 kHz/375 kHz 2.7 3.6
365 kHz/460 kHz 4.7 V
PWM only 1.5
VSKIPSEL SKIPSEL setting voltage Auto skip 1.9 2.1
OOA auto skip 2.7
PROTECTION: CURRENT SENSE
IENTRIP ENTRIPx source current VENTRIPx = 920 mV, TA= 25°C 9.4 10 10.6 μA
ENTRIPx current temperature
TCIENTRIP On the basis of 25°C(2) 4500 ppm/°C
coefficient ((VENTRIPx-GND/9)-24 mV -VGND-LLx) voltage,
VOCLoff OCP comparator offset -8 0 8
VENTRIPx-GND = 920 mV
VOCL(max) Maximum OCL setting VENTRIPx = 5 V 185 205 225 mV
Zero cross detection
VZC VGND-LLx voltage -5 0 5
comparator offset
VENTRIP Current limit threshold VENTRIPx-GND voltage, (2) 0.515 2 V
PROTECTION: UNDERVOLTAGE AND OVERVOLTAGE
VOVP OVP trip threshold OVP detect 110% 115% 120%
tOVPDEL OVP prop delay 2 μs
UVP detect 55% 60% 65%
VUVP Output UVP trip threshold Hysteresis 10%
tUVPDEL Output UVP prop delay 20 32 40 μs
tUVPEN Output UVP enable delay 1.4 2 2.6 ms
UVLO
Wake up 4.1 4.2 4.3
VUVVREG5 VREG5 UVLO threshold Hysteresis 0.38 0.43 0.48 V
VUVVREG3 VREG3 UVLO threshold Shutdown (2) VO2-1
THERMAL SHUTDOWN
Shutdown temperature (2) 150
TSDN Thermal shutdown threshold °C
Hysteresis (2) 10
(2) Ensured by design. Not production tested.
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DEVICE INFORMATION
Table 1. TERMINAL FUNCTIONS TABLE
TERMINAL I/O DESCRIPTION
NAME NO.
VIN 16 I High voltage power supply input for 5-V/3.3-V LDO.
GND 15 - Ground.
3.3-V power supply output. Connect 10-μF ceramic capacitor to Power GND near the device. A 1-μF
VREG3 8 O ceramic capacitor is acceptable when not loaded.
VREG5 17 O 5-V power supply output. Connect 33-μF ceramic capacitor to Power GND near the device.
VREF 3 O 2-V reference voltage output. Connect 220-nF to 1-μF ceramic capacitor to Signal GND near the device.
Master enable input.
Open : LDOs on, and ready to turn on VCLK and switcher channels.
EN0 13 I/O 620 kΩto GND : enable both LDOs, VCLK off and ready to turn on switcher channels. Power
consumption is almost the same as the case of VCLK = ON.
GND : disable all circuit
ENTRIP1 1 Channel 1 and Channel 2 enable and OCL trip setting pins.Connect resistor from this pin to GND to set
I/O threshold for synchronous RDS(on) sense. Short to ground to shutdown a switcher channel.
ENTRIP2 6
VO1 24 Output connection to SMPS. These terminals work as fixed voltage inputs and output discharge inputs.
I/O VO1 and VO2 also work as 5 V and 3.3 V switch over return power input respectively.
VO2 7
VFB1 2 SMPS feedback inputs. Connect with feedback resistor divider.
I
VFB2 5
PGOOD 23 O Power Good window comparator output for channel 1 and 2. (Logical AND)
Selection pin for operation mode:
OOA auto skip : Connect to VREG3 or VREG5
SKIPSEL 14 I Auto skip : Connect to VREF
PWM only : Connect to GND
On-time adjustment pin.
365 kHz/460 kHz setting : connect to VREG5
TONSEL 4 I 300 kHz/375 kHz setting : connect to VREG3
245 kHz/305 kHz setting : connect to VREF
200 kHz/250 kHz setting : connect to GND
DRVL1 19 Low-side N-channel MOSFET driver outputs. GND referenced drivers.
O
DRVL2 12
VBST1 22 Supply input for high-side N-channel MOSFET driver (boost terminal).
I
VBST2 9
DRVH1 21 High-side N-channel MOSFET driver outputs. LL referenced drivers.
O
DRVH2 10
LL1 20 Switch node connections for high-side drivers, current limit and control circuitry.
I
LL2 11
VCLK 18 O 270-kHz clock output for 15-V charge pump.
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TPS51125RGE
VO1
PGOOD
VO2
VREG3
VBST1
DRVL1
LL1
DRVH1
VBST2
DRVH2
LL2
DRVL2
EN0
ENTRIP2
VFB2
VREF
TONSEL
VFB1
ENTRIP1
SKIPSEL
GND
VIN
VCLK
VREG5
2
3
4
5
6
7 8 9 10 11
1
12
13
14
15
16
17
18
24 23 22 21 20 19
TPS51125
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SLUS786G –OCTOBER 2007–REVISED JUNE 2012
RGE PACKAGE (TOP VIEW)
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Functional Block Diagram
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SLUS786G –OCTOBER 2007–REVISED JUNE 2012
Switcher Controller Block
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VIN SUPPLY CURRENT2
vs
JUNCTION TEMPERATURE
0
1
2
3
4
5
6
7
8
9
-50 0 50 100 150
TJ- Junction Temperature - °C
IVIN2 - VIN Supply Current2 - mA
VIN SUPPLY CURRENT2
vs
INPUT VOLTAGE
0
1
2
3
4
5
6
7
8
9
5 10 15 20 25
VIN - Input Voltage - V
IVIN2 - VIN Supply Current2 - mA
VIN SUPPLY CURRENT1
vs
INPUT VOLTAGE
0
100
200
300
400
500
600
700
800
5 10 15 20 25
VIN - Input Voltage - V
IVIN1 - VIN Supply Current1 - mA
VIN SUPPLY CURRENT1
vs
JUNCTION TEMPERATURE
0
100
200
300
400
500
600
700
800
-50 0 50 100 150
TJ- Junction Temperature - °C
IVIN1 - VIN Supply Current1 - mA
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TYPICAL CHARACTERISTICS
Figure 1. Figure 2.
Figure 3. Figure 4.
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VIN SHUTDOWN CURRENT
vs
INPUT VOLTAGE
0
5
10
15
20
25
5 10 15 20 25
VIN - Input Voltage - V
IVINSDN - VIN Shutdown Current - mA
VIN SHUTDOWN CURRENT
vs
JUNCTION TEMPERATURE
0
5
10
15
20
25
-50 0 50 100 150
TJ- Junction Temperature - °C
IVINSDN - VIN Shutdown Current - mA
VINSTANDBY CURRENT
vs
INPUTVOLTAGE
0
50
100
150
200
250
5 10 15 20 25
VIN -InputVoltage-V
I – VINStandbyCurrent – nA
VINSTBY
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SLUS786G –OCTOBER 2007–REVISED JUNE 2012
TYPICAL CHARACTERISTICS (continued)
Figure 5. Figure 6.
Figure 7. Figure 8.
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SWITCHINGFREQUENCY
vs
INPUTVOLTAGE
0
100
200
300
400
500
6 8 10 12 14 16 18 20 22 24 26
VIN -InputVoltage-V
fSW - Swithching Frequency - kHz
TONSEL =GND
CH1
CH2
SWITCHINGFREQUENCY
vs
INPUTVOLTAGE
0
100
200
300
400
500
6 8 10 12 14 16 18 20 22 24 26
VIN -InputVoltage-V
fSW - Swithching Frequency - kHz
TONSEL =2V
CH1
CH2
VCLK FREQUENCY
vs
JUNCTION TEMPERATURE
175
200
225
250
275
300
325
-50 0 50 100 150
TJ- Junction Temperature - °C
fCLK - VCLK Frequency - kHz
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TYPICAL CHARACTERISTICS (continued)
Figure 9. Figure 10.
Figure 11. Figure 12.
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SWITCHINGFREQUENCY
vs
OUTPUTCURRENT
0
100
200
300
400
500
0.001 0.01 0.1 1 10
IOUT -OutputCurrent- A
fSW - Swithching Frequency - kHz
TONSEL =2V
CH2 Auto-skip
CH2OOA
CH2PWMOnly
CH1PWMOnly
CH1 Auto-skip
CH1OOA
SWITCHINGFREQUENCY
vs
OUTPUTCURRENT
0
100
200
300
400
500
0.001 0.01 0.1 1 10
IOUT -OutputCurrent- A
fSW - Swithching Frequency - kHz
TONSEL =GND
CH2 Auto-skip
CH2OOA
CH2PWMOnly
CH1PWMOnly
CH1 Auto-skip
CH1OOA
SWITCHINGFREQUENCY
vs
INPUTVOLTAGE
0
100
200
300
400
500
6 8 10 12 14 16 18 20 22 24 26
VIN -InputVoltage-V
fSW - Swithching Frequency - kHz
TONSEL =3.3V
CH1
CH2
SWITCHINGFREQUENCY
vs
INPUTVOLTAGE
0
100
200
300
400
500
6 8 10 12 14 16 18 20 22 24 26
VIN -InputVoltage-V
fSW - Swithching Frequency - kHz
TONSEL =5V
CH1
CH2
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TYPICAL CHARACTERISTICS (continued)
Figure 13. Figure 14.
Figure 15. Figure 16.
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VREG5 OUTPUT VOLTAGE
vs
OUTPUT CURRENT
4.90
4.95
5.00
5.05
0 20 40 60 80 100
IVREG5 - VREG5 Output Current - m A
VVREG5 - VREG5 Output Voltage - V
OVP/UVP THRESHOLD VOLTAGE
vs
JUNCTION TEMPERATURE
40
50
60
70
80
90
100
110
120
130
140
150
-50 0 50 100 150
TJ- Junction Temperature - °C
VOVP/VUVP - OVP/UVP Threshold - %
SWITCHINGFREQUENCY
vs
OUTPUTCURRENT
0
100
200
300
400
500
0.001 0.01 0.1 1 10
IOUT -OutputCurrent- A
fSW - Swithching Frequency - kHz
TONSEL =5V
CH2 Auto-skip
CH2OOA
CH2PWMOnly
CH1PWMOnly
CH1 Auto-skip
CH1OOA
SWITCHINGFREQUENCY
vs
OUTPUTCURRENT
0
100
200
300
400
500
0.001 0.01 0.1 1 10
IOUT -OutputCurrent- A
fSW - Swithching Frequency - kHz
TONSEL =3.3V
CH2 Auto-skip
CH2OOA
CH2PWMOnly
CH1PWMOnly
CH1 Auto-skip
CH1OOA
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TYPICAL CHARACTERISTICS (continued)
Figure 17. Figure 18.
Figure 19. Figure 20.
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3.3-VOUTPUTVOLTAGE
vs
OUTPUTCURRENT
3.240
3.270
3.300
3.330
3.360
0.001 0.01 0.1 1 10
IOUT2 -3.3-VOutputCurrent- A
VOUT2 - 3.3-V Output Voltage - V
PWMOnly
Auto-skip
OOA
5-VOUTPUTVOLTAGE
vs
OUTPUTCURRENT
4.950
4.975
5.000
5.025
5.050
5.075
0.001 0.01 0.1 1 10
IOUT1 -5-VOutputCurrent- A
VOUT1 - 5-V Output Voltage - V
PWMOnly
Auto-skip
OOA
VREG3 OUTPUT VOLTAGE
vs
OUTPUT CURRENT
3.2
3.25
3.3
3.35
0 20 40 60 80 100
IVREG3 - VREG3 Output Current - mA
VVREG3 - VREG3 Output Voltage - V
VREF OUTPUT VOLTAGE
vs
OUTPUT CURRENT
1.980
1.985
1.990
1.995
2.000
2.005
2.010
2.015
2.020
0 20 40 60 80 100
IVREF - VREF Output Current - mA
VVREF - VREF Output Voltage - V
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
TYPICAL CHARACTERISTICS (continued)
Figure 21. Figure 22.
Figure 23. Figure 24.
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Link(s): TPS51125
5-V EFFICIENCY
vs
OUTPUT CURRENT
0
20
40
60
80
100
0.001 0.01 0.1 1 10
IOUT1 - 5-V Output Current - A
h- Efficiency - %
Auto-skip
PWM Only
OOA
VIN=8V
VIN=12V
VIN=20V
3.3-V EFFICIENCY
vs
OUTPUT CURRENT
0
20
40
60
80
100
0.001 0.01 0.1 1 10
IOUT2 - 3.3-V Output Current - A
h- Efficiency - %
Auto-skip
PWM Only
OOA
5-V Switcher ON
VIN=8V
VIN=12V
VIN=20V
3.3-VOUTPUTVOLTAGE
vs
INPUTVOLTAGE
3.240
3.270
3.300
3.330
3.360
6 8 10 12 14 16 18 20 22 24 26
VIN -InputVoltage-V
VOUT2 - 3.3-V Output Voltage - V
IO=0A
IO=6A
5-VOUTPUTVOLTAGE
vs
INPUTVOLTAGE
4.950
4.975
5.000
5.025
5.050
5.075
6 8 10 12 14 16 18 20 22 24 26
VIN -InputVoltage-V
VOUT1 - 5-V Output Voltage - V
IO=0A
IO=6A
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
TYPICAL CHARACTERISTICS (continued)
Figure 25. Figure 26.
Figure 27. Figure 28.
16 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
ENTRIP1 (2V/div)
VOUT1 (2V/div)
PGOOD (5V/div)
ENTRIP2 (2V/div)
VOUT2 (2V/div)
PGOOD (5V/div)
VOUT1 (100mV/div)
IIND (5A/div)
IOUT1 (5A/div)
VOUT2 (100mV/div)
IIND (5A/div)
IOUT2 (5A/div)
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
TYPICAL CHARACTERISTICS (continued)
5-V Load Transient Response 3.3-V Load Transient Response
Figure 29. Figure 30.
5-V Startup Waveforms 3.3-V Startup Waveforms
Figure 31. Figure 32.
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Link(s): TPS51125
ENTRIP1 (5V/div)
VOUT1 (2V/div)
PGOOD (5V/div)
DRVL1 (5V/div)
ENTRIP2 (5V/div)
VOUT2 (2V/div)
PGOOD (5V/div)
DRVL2 (5V/div)
VOUT1 (200mV/div)
VREG5 (200mV/div)
VOUT2 (200mV/div)
VREG3 (200mV/div)
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
TYPICAL CHARACTERISTICS (continued)
5-V Switchover Waveforms 3.3-V Switchover Waveforms
Figure 33. Figure 34.
5-V Soft-stop Waveforms 3.3-V Soft-stop Waveforms
Figure 35. Figure 36.
18 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
APPLICATION INFORMATION
PWM Operations
The main control loop of the switch mode power supply (SMPS) is designed as an adaptive on-time pulse width
modulation (PWM) controller. It supports a proprietary D-CAP™ mode. D-CAP™ mode does not require external
compensation circuit and is suitable for low external component count configuration when used with appropriate
amount of ESR at the output capacitor(s).
At the beginning of each cycle, the synchronous top MOSFET is turned on, or becomes ‘ON’ state. This
MOSFET is turned off, or becomes ‘OFF’ state, after internal one shot timer expires. This one shot is determined
by VIN and VOUT to keep frequency fairly constant over input voltage range, hence it is called adaptive on-time
control. The MOSFET is turned on again when the feedback point voltage, VFB, decreased to match with internal
2-V reference. The inductor current information is also monitored and should be below the over current threshold
to initiate this new cycle. Repeating operation in this manner, the controller regulates the output voltage. The
synchronous bottom or the “rectifying” MOSFET is turned on at the beginning of each ‘OFF’ state to keep the
conduction loss minimum.The rectifying MOSFET is turned off before the top MOSFET turns on at next switching
cycle or when inductor current information detects zero level. In the auto-skip mode or the OOA skip mode, this
enables seamless transition to the reduced frequency operation at light load condition so that high efficiency is
kept over broad range of load current.
Adaptive On-Time Control and PWM Frequency
TPS51125 does not have a dedicated oscillator on board. However, the part runs with pseudo-constant
frequency by feed-forwarding the input and output voltage into the on-time, one-shot timer. The on-time is
controlled inverse proportional to the input voltage and proportional to the output voltage so that the duty ratio will
be kept as VOUT/VIN technically with the same cycle time. The frequencies are set by TONSEL terminal
connection as Table 2.
Table 2. TONSEL Connection and Switching Frequency
SWITCHING FREQUENCY
TONSEL CONNECTION CH1 CH2
GND 200 kHz 250 kHz
VREF 245 kHz 305 kHz
VREG3 300 kHz 375 kHz
VREG5 365 kHz 460 kHz
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Link(s): TPS51125
fSW
0
O
1
f2 ESR C 4
= £
p ´ ´
ESR
R1
Co
+
2V
+
Lx
R2
Control
logic
&
Driver
RL
VIN
VFB
DRVH
DRVL
PWM
Switching ModulatorVoltage Divider
IoIc
IL
Vc
Output Capacitor
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
Loop Compensation
From small-signal loop analysis, a buck converter using D-CAPTM mode can be simplified as below.
Figure 37. Simplifying the Modulator
The output voltage is compared with internal reference voltage after divider resistors, R1 and R2. The PWM
comparator determines the timing to turn on high-side MOSFET. The gain and speed of the comparator is high
enough to keep the voltage at the beginning of each on cycle substantially constant. For the loop stability, the
0dB frequency, f0, defined below need to be lower than 1/4 of the switching frequency.
(1)
As f0is determined solely by the output capacitor's characteristics, loop stability of D-CAPTM mode is determined
by the capacitor's chemistry. For example, specialty polymer capacitors (SP-CAP) have Co in the order of
several 100 μF and ESR in range of 10 mΩ. These will make f0in the order of 100 kHz or less and the loop will
be stable. However, ceramic capacitors have f0at more than 700 kHz, which is not suitable for this operational
mode.
Ramp Signal
The TPS51125 adds a ramp signal to the 2-V reference in order to improve its jitter performance. As described in
the previous section, the feedback voltage is compared with the reference information to keep the output voltage
in regulation. By adding a small ramp signal to the reference, the S/N ratio at the onset of a new switching cycle
is improved. Therefore the operation becomes less jitter and stable. The ramp signal is controlled to start with -
20mV at the beginning of ON-cycle and to become 0 mV at the end of OFF-cycle in steady state. By using this
scheme, the TPS51125 improve jitter performance without sacrificing the reference accuracy.
20 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
( )
f
IN OUT OUT
OUT(LL)
IN
1
I2 L
V V V
V
´
´ ´
- ´
=
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
Light Load Condition in Auto-Skip Operation
The TPS51125 automatically reduces switching frequency at light load conditions to maintain high efficiency.
This reduction of frequency is achieved smoothly and without increase of VOUT ripple. Detail operation is
described as follows. As the output current decreases from heavy load condition, the inductor current is also
reduced and eventually comes to the point that its ‘valley’ touches zero current, which is the boundary between
continuous conduction and discontinuous conduction modes. The rectifying MOSFET is turned off when this zero
inductor current is detected. As the load current further decreased, the converter runs in discontinuous
conduction mode and it takes longer and longer to discharge the output capacitor to the level that requires next
‘ON’ cycle. The ON time is kept the same as that in the heavy load condition. In reverse, when the output current
increase from light load to heavy load, switching frequency increases to the preset value as the inductor current
reaches to the continuous conduction. The transition load point to the light load operation IOUT(LL) (i.e. the
threshold between continuous and discontinuous conduction mode) can be calculated as follows;
(2)
where f is the PWM switching frequency.
Switching frequency versus output current in the light load condition is a function of L, VIN and VOUT, but it
decreases almost proportional to the output current from the IOUT(LL) given above. For example, it will be 60 kHz
at IOUT(LL)/5 if the frequency setting is 300 kHz.
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Link(s): TPS51125
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
Out-of-Audio™ Light-Load Operation
Out-of-Audio™ (OOA) light-load mode is a unique control feature that keeps the switching frequency above
acoustic audible frequencies toward virtually no load condition while maintaining best of the art high conversion
efficiency. When the Out-of-Audio™ operation is selected, OOA control circuit monitors the states of both
MOSFET and force to change into the ‘ON’ state if both of MOSFETs are off for more than 32 μs. This means
that the top MOSFET is turned on even if the output voltage is higher than the target value so that the output
capacitor is tends to be overcharged.
The OOA control circuit detects the over-voltage condition and begins to modulate the on time to keep the output
voltage regulated. As a result, the output voltage becomes 0.5% higher than normal light-load operation.
Enable and Soft Start
EN0 is the control pin of VREG5, VREG3 and VREF regulators. Bring this node down to GND disables those
three regulators and minimize the shutdown supply current to 10 μA. Pulling this node up to 3.3 V or 5 V will turn
the three regulators on to standby mode. The two switch mode power supplies (channel-1, channel-2) become
ready to enable at this standby mode. The TPS51125 has an internal, 1.6 ms, voltage servo softstart for each
channel. When the ENTRIPx pin becomes higher than the enable threshold voltage, which is typically 430 mV,
an internal DAC begins ramping up the reference voltage to the PWM comparator. Smooth control of the output
voltage is maintained during start up. As TPS51125 shares one DAC with both channels, if ENTRIPx pin
becomes higher than the enable threshold voltage while another channel is starting up, soft start is postponed
until another channel soft start has completed. If both of ENTRIP1 and ENTRIP2 become higher than the enable
threshold voltage at a same time (within 60 μs), both channels start up at same time.
Table 3. Enabling State
EN0 ENTRIP1 ENTRIP2 VREF VREG5 VREG3 CH1 CH2 VCLK
GND Don’t Care Don’t Care Off Off Off Off Off Off
R to GND Off Off On On On Off Off Off
R to GND On Off On On On On Off Off
R to GND Off On On On On Off On Off
R to GND On On On On On On On Off
Open Off Off On On On Off Off Off
Open On Off On On On On Off On
Open Off On On On On Off On Off
Open On On On On On On On On
VREG5/VREG3 Linear Regulators
There are two sets of 100-mA standby linear regulators which outputs 5 V and 3.3 V, respectively. The VREG5
serves as the main power supply for the analog circuitry of the device and provides the current for gate drivers.
The VREG3 is intended mainly for auxiliary 3.3-V supply for the notebook system during standby mode.
Add a ceramic capacitor with a value of at least 33 μF and place it close to the VREG5 pin, and add at most 10
μF to the VREG3 pin. Total capacitance connected to the VREG3 pin should not exceed 10 μF.
22 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
VREG5 Switch Over
When the VO1 voltage becomes higher than 4.7 V AND channel-1 internal powergood flag is generated, internal
5-V LDO regulator is shut off and the VREG5 output is connected to VO1 by internal switch over MOSFET. The
510-μs powergood delay helps a switch over without glitch.
VREG3 Switch Over
When the VO2 voltage becomes higher than 3.15 V AND channel-2 internal powergood flag is generated,
internal 3.3-V LDO regulator is shut off and the VREG3 output is connected to VO2 by internal switch over
MOSFET. The 510-μs powergood delay helps a switch over without glitch.
Powergood
The TPS51125 has one powergood output that indicates 'high' when both switcher outputs are within the targets
(AND gated). The powergood function is activated with 2-ms internal delay after ENTRIPx goes high. If the
output voltage becomes within +/-5% of the target value, internal comparators detect power good state and the
powergood signal becomes high after 510-μs internal delay. Therefore PGOOD goes high around 2.5 ms after
ENTRIPx goes high. If the output voltage goes outside of +/-10% of the target value, the powergood signal
becomes low after 2-μs internal delay. The powergood output is an open drain output and is needed to be pulled
up outside.
Also note that, in the case of Auto-skip or Out-of-Audio™ mode, if the output voltage goes +10% above the
target value and the power-good signal flags low, then the loop attempts to correct the output by turning on the
low-side driver (forced PWM mode). After the feedback voltage returns to be within +5% of the target value and
the power-good signal goes high, the controller returns back to auto-skip mode or Out-of-Audio™ mode.
Output Discharge Control
When ENTRIPx is low, the TPS51125 discharges outputs using internal MOSFET which is connected to VOx
and GND. The current capability of these MOSFETs is limited to discharge slowly.
Low-Side Driver
The low-side driver is designed to drive high current low RDS(on) N-channel MOSFET(s). The drive capability is
represented by its internal resistance, which are 4 Ωfor VREG5 to DRVLx and 1.5 Ωfor DRVLx to GND. A dead
time to prevent shoot through is internally generated between top MOSFET off to bottom MOSFET on, and
bottom MOSFET off to top MOSFET on. 5-V bias voltage is delivered from VREG5 supply. The instantaneous
drive current is supplied by an input capacitor connected between VREG5 and GND. The average drive current
is equal to the gate charge at Vgs = 5 V times switching frequency. This gate drive current as well as the high-
side gate drive current times 5 V makes the driving power which need to be dissipated from TPS51125 package.
High-Side Driver
The high-side driver is designed to drive high current, low RDS(on) N-channel MOSFET(s). When configured as a
floating driver, 5-V bias voltage is delivered from VREG5 supply. The average drive current is also calculated by
the gate charge at Vgs = 5 V times switching frequency. The instantaneous drive current is supplied by the flying
capacitor between VBSTx and LLx pins. The drive capability is represented by its internal resistance, which are
4Ωfor VBSTx to DRVHx and 1.5Ωfor DRVHx to LLx.
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Link(s): TPS51125
18
1uF
100nF
100nF
100nF
PGND PGND PGND
- 15V/10mA
D0 D1 D2 D4
100nF
VO1(5V)
VCLK
3.3V
13
TPS51125
EN0
13
TPS51125
EN0
Control
Input
Control
Input
15
GND
15
GND
(a) Control by MOSFET switch (b) Control by Logic
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
VCLK for Charge Pump
270-kHz clock signal can be used for charge pump circuit to generate approximately 15-V dc voltage. The clock
signal becomes available when EN0 becomes higher than 2.4 V or open state. Example of control circuit is
shown in Figure 38. Note that the clock driver uses VO1 as its power supply. Regardless of enable or disable of
VCLK, power consumption of the TPS51125 is almost the same. Therefore even if VCLK is not used, one can let
EN0 pin open or supply logic ‘high’, as shown in Figure 38, and let VCLK pin open. This approach further
reduces the external part count.
Figure 38. Control Example of EN0 Master Enable
Figure 39. 15-V / 10-mA Charge Pump Configuration
24 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
( ) ( )
( )
f
IN OUT OUT
TRIP RIPPLE TRIP
OCP
IN
DS on DS on
V V V
V I V 1
IR 2 R 2 L V
- ´
= + = + ´
´ ´
( ) ( ) ( ) ( )
TRIP TRIP
TRIP
R k I A
V mV 24 mV
9
W ´ m
= -
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
Current Protection
TPS51125 has cycle-by-cycle over current limiting control. The inductor current is monitored during the ‘OFF’
state and the controller keeps the ‘OFF’ state during the inductor current is larger than the over current trip level.
In order to provide both good accuracy and cost effective solution, TPS51125 supports temperature
compensated MOSFET RDS(on) sensing. ENTRIPx pin should be connected to GND through the trip voltage
setting resistor, RTRIP. ENTRIPx terminal sources ITRIP current, which is 10 μA typically at room temperature, and
the trip level is set to the OCL trip voltage VTRIP as below. Note that the VTRIP is limited up to about 205 mV
internally.
(3)
External leakage current to ENTRIPx pin should be minimized to obtain accurate OCL trip voltage.
The inductor current is monitored by the voltage between GND pin and LLx pin so that LLx pin should be
connected to the drain terminal of the bottom MOSFET properly. Itrip has 4500 ppm/°C temperature slope to
compensate the temperature dependency of the RDS(on). GND is used as the positive current sensing node so
that GND should be connected to the proper current sensing device, i.e. the source terminal of the bottom
MOSFET.
As the comparison is done during the ‘OFF’ state, VTRIP sets valley level of the inductor current. Thus, the load
current at over current threshold, IOCP, can be calculated in Equation 4.
(4)
In an overcurrent condition, the current to the load exceeds the current to the output capacitor thus the output
voltage tends to fall down. Eventually, it ends up with crossing the under voltage protection threshold and
shutdown both channels.
Over/Under Voltage Protection
TPS51125 monitors a resistor divided feedback voltage to detect over and under voltage. When the feedback
voltage becomes higher than 115% of the target voltage, the OVP comparator output goes high and the circuit
latches as the top MOSFET driver OFF and the bottom MOSFET driver ON.
Also, TPS51125 monitors VOx voltage directly and if it becomes greater than 5.75 V the TPS51125 turns off the
top MOSFET driver.
When the feedback voltage becomes lower than 60% of the target voltage, the UVP comparator output goes
high and an internal UVP delay counter begins counting. After 32 μs, TPS51125 latches OFF both top and
bottom MOSFETs drivers, and shut off both drivers of another channel. This function is enabled after 2 ms
following ENTRIPx has become high.
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Link(s): TPS51125
( ) ( )
( )
( )
( )
f
OUT
RIPPLE
V 20 mV 1 D 20 mV L
ESR 2 V I 2 V
´ ´ - ´ ´
= =
´
( ) ( )
( )
()
( )
f
OUT OUT
IN max
TRIP
IND peak
DS on IN max
V1
R L
V V V
IV´
- ´
= + ´
( )
( )
()
( ) ( )
( )
()
( )
f f
OUT OUT OUT OUT
IN max IN max
IND ripple IN max OUT max IN max
1 3
I I
V V V V V V
LV V
´
´ ´
- ´ - ´
= = ´
( )
OUT
V 2.0
R1 R2
2.0
-
= ´
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
UVLO Protection
TPS51125 has VREG5 under voltage lock out protection (UVLO). When the VREG5 voltage is lower than UVLO
threshold voltage both switch mode power supplies are shut off. This is non-latch protection. When the VREG3
voltage is lower than (VO2 - 1 V), both switch mode power supplies are also shut off.
Thermal Shutdown
TPS51125 monitors the temperature of itself. If the temperature exceeds the threshold value (typically 150°C),
TPS51125 is shut off including LDOs. This is non-latch protection.
External Parts Selection
The external components selection is much simple in D-CAP™ Mode.
1. Determine Output Voltage
The output voltage is programmed by the voltage-divider resistor, R1 and R2 shown in Figure 37. R1 is
connected between VFBx pin and the output, and R2 is connected betwen the VFBx pin and GND.
Recommended R2 value is from 10 kΩto 20 kΩ. Determine R1 using equation as below.
(5)
2. Choose the Inductor
The inductance value should be determined to give the ripple current of approximately 1/4 to 1/2 of maximum
output current. Larger ripple current increases output ripple voltage and improves S/N ratio and helps stable
operation.
(6)
The inductor also needs to have low DCR to achieve good efficiency, as well as enough room above peak
inductor current before saturation. The peak inductor current can be estimated as follows.
(7)
3. Choose the Output Capacitor(s)
Organic semiconductor capacitor(s) or specialty polymer capacitor(s) are recommended. Determine ESR to meet
required ripple voltage. A quick approximation is as shown in Equation 8.
where
• D is the duty cycle
• the required output ripple slope is approximately 20 mV per tSW (switching period) in terms of VFB terminal
voltage (8)
4. Choose the Low-Side MOSFET
It is highly recommended that the low-side MOSFET should have an integrated Schottky barrier diode, or an
external Schottky barrier diode in parallel to achieve stable operation.
26 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
Layout Considerations
Certain points must be considered before starting a layout work using the TPS51125.
• TPS51125 has only one GND pin and special care of GND trace design makes operation stable, especially
when both channels operate. Group GND terminals of output voltage divider of both channels and the VREF
capacitor as close as possible, connect them to an inner GND plane with PowerPad, overcurrent setting
resistor, EN0 pull-down resistor and EN0 bypass capacitor as shown in the thin GND line of Figure 40. This
trace is named Signal Ground (SGND). Group ground terminals of VIN capacitor(s), VOUT capacitor(s) and
source of low-side MOSFETs as close as possible, and connect them to another inner GND plane with GND
pin of the device, GND terminal of VREG3 and VREG5 capacitors and 15-V charge-pump circuit as shown in
the bold GND line of Figure 40. This trace is named Power Ground (PGND). SGND should be connected to
PGND at the middle point between ground terminal of VOUT capacitors.
• Inductor, VOUT capacitor(s), VIN capacitor(s) and MOSFETs are the power components and should be
placed on one side of the PCB (solder side). Power components of each channel should be at the same
distance from the TPS51125. Other small signal parts should be placed on another side (component side).
Inner GND planes above should shield and isolate the small signal traces from noisy power lines.
• PCB trace defined as LLx node, which connects to source of high-side MOSFET, drain of low-side MOSFET
and high-voltage side of the inductor, should be as short and wide as possible.
• VREG5 requires capacitance of at least 33 μF and VREG3 requires capacitance of at most 10 μF. VREF
requires a 220-nF ceramic bypass capacitor which should be placed close to the device and traces should be
no longer than 10 mm.
• Connect the overcurrent setting resistors from ENTRIPx to SGND and close to the device, right next to the
device if possible.
• The discharge path (VOx) should have a dedicated trace to the output capacitor; separate from the output
voltage sensing trace. When LDO5 is switched over Vo1 trace should be 1.5 mm with no loops. When LDO3
is switched over and loaded Vo2 trace should also be 1.5 mm with no loops. There is no restriction for just
monitoring Vox. Make the feedback current setting resistor (the resistor between VFBx to SGND) close to the
device. Place on the component side and avoid vias between this resistor and the device.
• Connections from the drivers to the respective gate of the high-side or the low-side MOSFET should be as
short as possible to reduce stray inductance. Use 0.65-mm (25 mils) or wider trace and via(s) of at least 0.5
mm (20 mils) diameter along this trace.
• All sensitive analog traces and components such as VOx, VFBx, VREF, GND, EN0, ENTRIPx, PGOOD,
TONSEL and SKIPSEL should be placed away from high-voltage switching nodes such as LLx, DRVLx,
DRVHx and VCLK nodes to avoid coupling.
• Traces for VFB1 and VFB2 should be short and laid apart each other to avoid channel to channel
interference.
• In order to effectively remove heat from the package, prepare thermal land and solder to the package’s
thermal pad. Three by three or more vias with a 0.33-mm (13 mils) diameter connected from the thermal land
to the internal ground plane should be used to help dissipation. This thermal land underneath the package
should be connected to SGND, and should NOT be connected to PGND.
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 27
Product Folder Link(s): TPS51125
TPS51125
DRVL1DRVL2
PowerPAD
VFB1VFB2 VREF
GND
VREG5 VREG3
220 nF
SGND
SGND
UDG-09020
532
12 19
15
33 mF
817
10 mF
VIN
VIN
VOUT1
VOUT2
PGND PGND
Charge
Pump
VCLK
15 V
OUT
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
Figure 40. Ground System
28 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
Driver and switch node traces are shown for CH1 only.
*
Cin
Cin
L
L
Vout1
HS-MOSFET
LS-MOSFET
HS-MOSFET
Vout2
Cout
To CH1 Vout divider
To CH2 Vout divider
To VO2
To VO1
LS-MOSFET
Bottom Layer
VIN
GND
Connection to GND island
Connection to GND
Connection of Vout
Top Layer
TPS51125
CVREF
CH1 Vout divider
CVREG5
DRVH1*
LL1*
DRVL1*
Through hole
CH2 Vout divider Connection to
GND island
GND
Inner Layer
CVREG3
Cout
GND island
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
Figure 41. PCB Layout
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Link(s): TPS51125
9
10
11
12
VO1
PGOOD
VO2
VREG3
TPS51125RGE
(QFN24)
13 14 15 16
VBST1
DRVL1
LL1
DRVH1
VBST2
DRVH2
LL2
DRVL2
17
EN0
8
ENTRIP2
7
6
VFB2
5
VREF
4
TONSEL
3
VFB1
2 1
ENTRIP1
18
SKIPSEL
19
20
GND
21
VIN
22
23
24
VCLK
VO1
5V/8A
L2
3.3mH
Q3
IRF7821
VO1_GND
PGND
C9
10mF
C7
0.1mF
VIN
VO2
3.3V/8A
L1
3.3mH
Q1
IRF7821
VO2_GND
C4
0.1mF
VIN
PowerPAD
C11
33mF
VREG5
C10
POSCAP
330mF
PGND
R9
5.1W
VIN
5.5~28V
R7
5.1W
C2
10mF
C1
10mF
PGND
C5
POSCAP
330mF
5V/100mA
PGND
R4
30kW
R2
20kW
R1
13kW
SGND
VREG5
VREG5
R8
100kW
PGND
R3
20kW
C6
0.22mF
PGND
SGND
R6
130kW
SGND
R5
130kW
C16
1uF
C13
100nF
C14
100nF
C15
100nF
PGND
15V/10mA
D1
D2
D3
D4
C12
100nF
C3
10mF
PGND
3.3V/100mA
C8
10mF
VREF VO1
EN0
PGNDPGND
SGND
VREF
R10
620kW
S1
SGND
Q2
FDS6690AS Q4
FDS6690AS
TPS51125
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
www.ti.com
Application Circuit
Figure 42. 5-V/8-A, 3.3-V/8-A Application Circuit (245-kHz/305-kHz Setting)
Table 4. List of Materials for 5-V/8-A, 3.3-V/8-A Application Circuit
SYMBOL SPECIFICATION MANUFACTURER PART NUMBER
C1, C2, C8, C9 10 μF, 25 V Taiyo Yuden TMK325BJ106MM
C3 10 μF, 6.3 V TDK C2012X5R0J106K
C11 33 μF, 6.3 V TDK C3216X5RBJ336M
C5, C10 330 μF, 6.3 V, 25 mΩSanyo 6TPE330ML
3.3 μH, 15.6 A, 5.92
L1, L2 TOKO FDA1055-3R3M
mΩ
Q1, Q3 30 V, 9.5 mΩIR IRF7821
Q2, Q4(1) 30 V, 12 mΩFairchild FDS6690AS
(1) Please use MOSFET with integrated Schottky barrier diode (SBD) for low side, or add SBD in parallel
with normal MOSFET.
30 Submit Documentation Feedback Copyright © 2007–2012, Texas Instruments Incorporated
Product Folder Link(s): TPS51125
TPS51125
www.ti.com
SLUS786G –OCTOBER 2007–REVISED JUNE 2012
REVISION HISTORY
Changes from Revision E (May 2011) to Revision F Page
• Added Input voltage range parameter, LL1, LL2, pulse width < 20 ns with a value of -5 V to 30 V. ................................... 2
Changes from Revision F (March 2012) to Revision G Page
• Added electrostatic discharge ratings in ABSOLUTE MAXIMUM RATINGS table .............................................................. 2
Copyright © 2007–2012, Texas Instruments Incorporated Submit Documentation Feedback 31
Product Folder Link(s): TPS51125
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
TPS51125RGER VQFN RGE 24 3000 330.0 12.4 4.25 4.25 1.15 8.0 12.0 Q2
TPS51125RGER VQFN RGE 24 3000 330.0 12.4 4.3 4.3 1.1 8.0 12.0 Q2
TPS51125RGER VQFN RGE 24 3000 330.0 12.4 4.25 4.25 1.15 8.0 12.0 Q2
TPS51125RGET VQFN RGE 24 250 180.0 12.4 4.25 4.25 1.15 8.0 12.0 Q2
TPS51125RGET VQFN RGE 24 250 180.0 12.4 4.25 4.25 1.15 8.0 12.0 Q2
TPS51125RGET VQFN RGE 24 250 180.0 12.4 4.3 4.3 1.1 8.0 12.0 Q2
PACKAGE MATERIALS INFORMATION
www.ti.com 14-Jul-2012
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
TPS51125RGER VQFN RGE 24 3000 367.0 367.0 35.0
TPS51125RGER VQFN RGE 24 3000 370.0 355.0 55.0
TPS51125RGER VQFN RGE 24 3000 367.0 367.0 35.0
TPS51125RGET VQFN RGE 24 250 210.0 185.0 35.0
TPS51125RGET VQFN RGE 24 250 210.0 185.0 35.0
TPS51125RGET VQFN RGE 24 250 195.0 200.0 45.0
PACKAGE MATERIALS INFORMATION
www.ti.com 14-Jul-2012
Pack Materials-Page 2
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