Deadtime Control

Low-Side Gate Driver (LSG)

Integrated Pulldown MOSFET

L(H) +

VO

1 *

VO

VI

ƒs 0.6

(7)

Thermal Shutdown

Overcurrent Protection

T

HICCUP

(ms) +

2250

ƒs (kHz)

(8)

TPS54352-EP

,, TPS54353-EP,, TPS54354-EP

TPS54355-EP

, TPS54356-EP, TPS54357-EP

Adaptive dead-time control prevents shoot-through current from flowing in the integrated high-side MOSFET and

the external low-side MOSFET during the switching transitions by actively controlling the turn-on times of the

drivers. The high-side driver does not turn on until the voltage at the gate of the low-side MOSFET is below 1 V.

The low-side driver does not turn on until the voltage at the gate of the high-side MOSFET is below 1 V.

LSG is the output of the low-side gate driver. The 100-mA MOSFET driver is capable of providing gate drive for

most popular MOSFETs suitable for this application. Use the SWIFT Designer Software Tool to find the most

appropriate MOSFET for the application. Connect the LSG pin directly to the gate of the low-side MOSFET. Do

not use a gate resistor, as the resulting turn-on time may be too slow.

The TPS5435x has a diode-MOSFET pair from PH to PGND. The integrated MOSFET is designed for light-load

continuous-conduction-mode operation when only an external Schottky diode is used. The combination of

devices keeps the inductor current continuous under conditions where the load current drops below the inductor's

critical current. Care should be taken in the selection of inductor in applications using only a low-side Schottky

diode. Since the inductor ripple current flows through the integrated low-side MOSFET at light loads, the

inductance value should be selected to limit the peak current to less than 0.3 A during the high-side FET turn-off

time. The minimum value of inductance is calculated using the following equation:

The device uses the thermal shutdown to turn off the MOSFET drivers and controller if the junction temperature

exceeds 165°C. The device is restarted automatically when the junction temperature decreases to 7°C below the

thermal shutdown trip point and starts up under control of the slow-start circuit.

Overcurrent protection is implemented by sensing the drain-to-source voltage across the high-side MOSFET and

compared to a voltage level that represents the overcurrent threshold limit. If the drain-to-source voltage exceeds

the overcurrent threshold limit for more than 100 ns, the ENA pin is pulled low, the high-side MOSFET is

disabled, and the internal digital slow-start is reset to 0 V. ENA is held low for approximately the time that is

calculated by the following equation:

Once the hiccup time is complete, ENA is released and the converter initiates the internal slow start.

Copyright © 2007–2009, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Link(s): TPS54352-EP TPS54353-EP TPS54354-EP TPS54355-EP TPS54356-EP TPS54357-EP