TPS65257

www.ti.com

SLVSB32

– SEPTEMBER 2011

4.5-V TO 16-V INPUT, HIGH CURRENT, SYNCHRONOUS STEP DOWN THREE DC-DC

CONVERTER WITH INTEGRATED FET, USB SWITCH AND PUSH BUTTON CONTROL

Check for Samples: TPS65257

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FEATURES

•

Current-Mode Control With Simple

Compensation Circuit

•

Wide Input Supply Voltage Range:

•

Automatic Low Pulse Skipping (PSM) Power

4.5 V - 16 V

Mode, Allowing for an Output Ripple Better

•

0.8-V, 1% Accuracy Reference

than 2%

•

Continuous Loading:

•

Support Pre-Biased Outputs

3 A (Buck1), 2 A (Buck2 and 3)

•

Power Good Supervisor and Reset Generator

•

Maximum Current:

•

1-A USB Power Switch With Overcurrent and

3.5 A (Buck 1), 2.5 A (Buck2 and 3)

Thermal Protection

•

Synchronous Operation, 300-kHz

– 2.2-MHz

•

Push Button (10-kV ESD Rated Pin for PB_IN)

Switching Frequency Set By External Resistor

Control for Intelligent System

•

External Enable Pins With Built-In Current

Power-On/Power-Off Operation

Source for Easy Sequencing

•

Small, Thermally Efficient 40-Pin 6-mm x 6-mm

•

External Soft Start Pins

RHA (QFN) package

•

Adjustable Cycle-by-Cycle Current Limit Set

•

-40

°C to 125°C Junction Temperature Range

by External Resistor

DESCRIPTION/ORDERING INFORMATION

TPS65257 is a power management IC with three step-down buck converters. Both high-side and low-side

MOSFETs are integrated to provide fully synchronous conversion with higher efficiency. The converters are

designed to simplify its application while giving the designer the option to optimize their usage according to the

target application.

The converters can operate in 5-, 9-, 12- or 15-V systems. The output voltage can be set externally using a

resistor divider to any value between 0.8 V and the input supply minus the resistive drops on the converter path.

Each converter features enable pin that allows a delayed start-up for sequencing purposes, soft start pin that

allows adjustable soft-start time by choosing the soft-start capacitor, and a current limit (RLIM) pin that enables

designer to adjust current limit by selecting an external resistor and optimize the choice of inductor. All converters

operate in

‘hiccup mode’: Once an over-current lasting more than 10 ms is sensed in any of the converters, they

will shut down for 10 ms and then the start-up sequencing will be tried again. If the overload has been removed,

the converter will ramp up and operate normally. If this is not the case the converter will see another over-current

event and shuts down again repeating the cycle (hiccup) until the failure is cleared. If an overload condition lasts

for less than 10 ms, only the relevant converter affected will shut-down and re-start and no global hiccup mode

will occur.

The switching frequency of the converters is set by an external resistor connected to ROSC pin. The switching

regulators are designed to operate from 300 kHz to 2.2 MHz. The converters operate with 180

° phase between

then to minimize the input filter requirements.

All converters have peak current mode control which simplifies external frequency compensation. The device has

a built-in slope compensation ramp. The slope compensation can prevent sub harmonic oscillations in peak

current mode control. A traditional type II compensation network can stabilize the system and achieve fast

transient response. Moreover, an optional capacitor in parallel with the upper resistor of the feedback divider

provides one more zero and makes the crossover frequency over 100 kHz.

All converters feature an automatic low power pulse PFM skipping mode which improves efficiency during light

loads and standby operation, while guaranteeing a very low output ripple, allowing for a value of less than 2% at

low output voltages.

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Please 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.

PRODUCTION DATA information is current as of publication date.

Copyright

© 2011, 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.