1.167

OSC

SW

R

(k

)

21.82 f

-

W =

×

TPS5403

SLVSBK5 – SEPTEMBER 2012

www.ti.com

OVERVIEW

The TPS5403 is a 28-V, 1.7-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 TPS5403’s switching frequency is adjustable with an external resistor or fixed by connecting the frequency

program pin to GND or leaving it unconnected.

and under no load. When the device is disabled, the supply current is 1

μA typically.

The integrated 120-m

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

output currents up to 1.7 A.

The TPS5403 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 pins. 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 2.1 V typically.

By adding an external capacitor, the slow start time of the TPS5403 can be adjustable which enables flexible

output filter selection. To improve the efficiency at light load conditions, the TPS5403 enters a special pulse

skipping mode when the peak inductor current drops below 300 mA 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

Adjustable Frequency PWM Control

The TPS5403 uses an external resistor to adjust the switching frequency. Connecting the ROSC pin to ground

fixes the switching frequency at 70 kHz, leaving it open gives 120-kHz switching frequency.

Figure 11. ROSC vs Switching Frequency

(1)

For operation at 300 kHz, an 85.5-k

Ω resistor is required.

8

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