1

3

PH

9

BOOT

Boot

UVLO

Regulator

Power Stage

and Dead-Time

Control Logic

LS MOSFET

Current Limit

Oscillator

10

RT

Exposed Thermal Pad

4/5

Current

Sense

Slope

Compensation

HS MOSFET

Current

Comparator

Current

Sense

Boot

Charge

Minimum

Clamp Pulse

Skip

UVLO

Thermal

Hiccup

Shutdown

Logic

+

+

Maximum

Clamp

Overload

Recovery

7

COMP

+

Voltage

Reference

6

VSENSE

Hiccuup

Shutdown

0 V

Error

Amplifier

Hiccuup

Shutdown

VIN

8

EN

Enable

Threshold

Copyright © 2016, Texas Instruments Incorporated

10

TPS54335-2A

SLUSCK3 – JULY 2016

www.ti.com

Product Folder Links: TPS54335-2A

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Copyright © 2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The device is a 28-V, 3-A, synchronous step-down (buck) converter with two integrated n-channel MOSFETs. To

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

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

The device has been designed for safe monotonic startup into pre-biased loads. The device has a typical default

startup voltage of 4 V. The EN pin has an internal pullup-current source that can provide a default condition when

the EN pin is floating for the device to operate. The total operating current for the device is 310 µA (typical) when

not switching and under no load. When the device is disabled, the supply current is less than 5 μA.

The integrated 128-m

Ω and 84-mΩ MOSFETs allow for high-efficiency power-supply designs with continuous

output currents up to 3 A.

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

the integrated high-side MOSFET is supplied by a capacitor between the BOOT and PH pins. The boot capacitor

voltage is monitored by an UVLO circuit and turns off the high-side MOSFET when the voltage falls below a

preset threshold. The output voltage can be stepped down to as low as the 0.8-V reference voltage.

The device minimizes excessive output overvoltage transients by taking advantage of the overvoltage power-

good comparator. When the regulated output voltage is greater than 106% of the nominal voltage, the

overvoltage comparator is activated, and the high-side MOSFET is turned off and masked from turning on until

the output voltage is lower than 104%.

The TPS54335–2A device has a wide switching frequency of 50 kHz to 1500 kHz which allows for efficiency and

size optimization when selecting the output filter components. The internal 2-ms soft-start time is implemented to

minimize inrush currents.

7.2 Functional Block Diagram