TPS54531

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SLVSBI5 – MAY 2013

OVERVIEW

The TPS54531 is a 28-V, 5-A, step-down (buck) converter with an integrated high-side n-channel MOSFET. To

improve performance during line and load transients, the device implements a constant frequency, current mode

control which reduces output capacitance and simplifies external frequency compensation design. The

TPS54531 has a pre-set switching frequency of 570kHz.

The TPS54531 needs a minimum input voltage of 3.5V to operate normally. 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 operating current is 110

μA typically when not switching and under no load. When the device is

disabled, the supply current is 1

μA typically.

The integrated 80 m

Ω high-side MOSFET allows for high efficiency power supply designs with continuous output

currents up to 5A.

The TPS54531 reduces the external component count by integrating the boot recharge diode. The bias voltage

for the integrated high-side MOSFET is supplied by an external capacitor on the BOOT to PH pin. The boot

capacitor voltage is monitored by an UVLO circuit and will turn the high-side MOSFET off when the voltage falls

below a preset threshold of 2.1V typically. The output voltage can be stepped down to as low as the reference

voltage.

By adding an external capacitor, the slow start time of the TPS54531 can be adjustable which enables flexible

output filter selection.

when the peak inductor current drops below 160mA typically.

The frequency foldback reduces the switching frequency during startup and over current conditions to help

control the inductor current. The thermal shut down gives the additional protection under fault conditions.

DETAILED DESCRIPTION

FIXED FREQUENCY PWM CONTROL

The TPS54531 uses a fixed frequency, peak current mode control. The internal switching frequency of the

TPS54531 is fixed at 570kHz.

ECO-MODE

TM

efficiency. When the peak inductor current is lower than 160 mA typically, the COMP pin voltage falls to 0.5 V

clamped at 0.5V internally which prevents the high side integrated MOSFET from switching. The peak inductor

integrated current comparator catches the peak inductor current only, the average load current entering Eco-

The voltage reference system produces a ±2% initial accuracy voltage reference (±3.5% over temperature) by

scaling the output of a temperature stable bandgap circuit. The typical voltage reference is designed at 0.8V.

BOOTSTRAP VOLTAGE (BOOT)

The TPS54531 has an integrated boot regulator and requires a 0.1

μF ceramic capacitor between the BOOT and

PH pin to provide the gate drive voltage for the high-side MOSFET. A ceramic capacitor with an X7R or X5R

grade dielectric is recommended because of the stable characteristics over temperature and voltage. To improve

drop out, the TPS54531 is designed to operate at 100% duty cycle as long as the BOOT to PH pin voltage is

greater than 2.1 V typically.

Copyright © 2013, Texas Instruments Incorporated

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