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LP8728

FB_B1

SW_B1

V

OUT1

FB_B2

SW_B2

V

OUT2

FB_B3

SW_B3

V

OUT3

FB_B4

SW_B4

V

OUT4

1.5µH

1.5µH

AG

N

D

G

N

D

_B1

G

N

D

_B2

G

N

D

_

B3

G

N

D

_B4

EN_B1

EN_B2

EN_B3

EN_B4

PG_B1

PG_B2

PG_B3

PG_B4

Micro 

Controller

DEFSEL

AVDD

BYP

V

IN

V

IN

VIN_B1

V

IN

VIN_B2

1.5µH

1.5µH

V

IN

V

IN

VIN_B3

VIN_B4

VDDIO

1µF

1µF

10µF

10µF

10µF

10µF

10µF

10µF

10µF

10µF

Chapter 2

SNVU231 – August 2013

Description of LP8728

The LP8728 is a quad output Power Management Unit, optimized for low power FPGAs, microprocessors,
and DSPs. This device integrates four highly efficient step-down DC/DC converters into one package. All
the converters run at fixed 3.3 MHz switching frequency. Buck converters switching is phase shifted to
minimize the input current spiking.

2.1

Features

Four High-Efficiency Step-Down DC/DC Converters

Max output current 1.0 A

Forced PWM operation

Soft-start control

V

OUT1

= 3.3 V

V

OUT2

- 1.25 V

V

OUT3

= 1.8 V or 2.65 V (pin selectable)

V

OUT4

= 1.8 V

Separate Enable Inputs for each Converter Control

Separate Power Good Outputs for each Converter

Output Over-Current and Input Over-Voltage Protection

Over-Temperature Protection

Under-Voltage Lockout (UVLO)

28-pin 0.5 mm Pitch QFN Package

2.2

Applications

Automotive Systems

Figure 2-1. Typical Application

3

SNVU231 – August 2013

Description of LP8728

Submit Documentation Feedback

Copyright © 2013, Texas Instruments Incorporated

Summary of Contents for LP8728EVM

Page 1: ...Using the LP8728EVM Evaluation Module User s Guide Literature Number SNVU231 August 2013 ...

Page 2: ...o facilitate ease of testing and evaluation of this circuit the LP8728EVM contains screw in terminals for the VIN and all four VOUT connections Dual connectors are provided for easy four wire connection For evaluation purposes the LP8728EVM has been tested over a 4 5 V to 5 5 V input range Users are cautioned to evaluate their specific operating conditions and choose components with the appropriat...

Page 3: ... All the converters run at fixed 3 3 MHz switching frequency Buck converters switching is phase shifted to minimize the input current spiking 2 1 Features Four High Efficiency Step Down DC DC Converters Max output current 1 0 A Forced PWM operation Soft start control VOUT1 3 3 V VOUT2 1 25 V VOUT3 1 8 V or 2 65 V pin selectable VOUT4 1 8 V Separate Enable Inputs for each Converter Control Separate...

Page 4: ...ent Two output terminals are connected in parallel so either one can be used for sense or force lines Connector X3 terminals VDDIOX and GND can be used to connect separated pull up voltage for the EN_Bx and DEFSEL pins If separated pull up voltage is not desired input pins can be pulled up to VIN voltage Pull up voltage is selected by changing the shunt position on the J2 terminal Connecting shunt...

Page 5: ...31 August 2013 Board Layout Figure 4 1 Layer 1 Top Signal Figure 4 2 Layer 2 GND Picture in reverse colors 5 SNVU231 August 2013 Board Layout Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Page 6: ...www ti com Figure 4 3 Layer 2 GND VIN Figure 4 4 Layer 4 Bottom Signal 6 Board Layout SNVU231 August 2013 Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Page 7: ...www ti com Figure 4 5 Close up of the LP8728 and Main External Components 7 SNVU231 August 2013 Board Layout Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Page 8: ... board FR4 Top layer 1 copper 35µm Prepreg 0 1 mm Internal Layer 2 35 µm Core 0 7 mm Ground plane Layer 3 35 µm Prepreg 0 1 mm Bottom Layer 4 copper 35 µm Surface finish immersion gold 8 Board Stackup SNVU231 August 2013 Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Page 9: ...f desired output voltage due to for example an overload condition the corresponding power good pin is set low 6 1 LP8728EVM Control Interface Figure 6 1 LP8728EVM Control Pins All LP8728 digital input and out signals are routed to 20 pin connector J3 pins Pins closer to PCB edge go straight to the LP8728 digital pins These pins can be used to connect LP8728 pins to any external source signal gener...

Page 10: ... SNVU231 August 2013 Evaluation Board Schematic Figure 7 1 Evaluation Board Schematic 10 Evaluation Board Schematic SNVU231 August 2013 Submit Documentation Feedback Copyright 2013 Texas Instruments Incorporated ...

Page 11: ... Gold J1 1 TSW 102 07 G S TSW 102 07 G S Samtec Inc plated Header 100mil 3x1 Gold J2 1 TSW 103 07 G S TSW 103 07 G S Samtec Inc plated Header 100mil 10x2 Gold J3 1 TSW 110 07 G D TSW 110 07 G D Samtec Inc plated L1 L2 L3 L4 4 1 5uH 1 1uH 2 0x2 5x1 2 MDT2520 CN1R5M Toko RES 0 01 ohm 1 3W CRA2512 FZ R1 1 0 01 High Power Current Sense 2512 Bourns R010ELF Chip Resistor R2 R3 R4 R5 RES 1 8k ohm 5 0 1W ...

Page 12: ...esponsible for compliance with all legal regulatory and safety related requirements concerning its products and any use of TI components in its applications notwithstanding any applications related information or support that may be provided by TI Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failur...

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