A6902D Просмотр технического описания (PDF) - STMicroelectronics

Номер в каталоге

Компоненты Описание

производитель

A6902D

Up to 1 A step down switching regulator with adjustable current limit for automotive applications

STMicroelectronics 

A6902D

Thermal shutdown

In fact, when the current of the power element is equal to the inductor current, the diode turns OFF and the drain

of the PDMOS is able to go high. But during its recovery time, the diode can be considered a high value capacitor

and this produces a very high peak current, responsible for numerous problems:

• Spikes on the device supply voltage that cause oscillations (and thus noise) due to the board parasites.

• Turn ON overcurrent leads to a decrease in the efficiency and system reliability.

• Major EMI problems.

• Shorter freewheeling diode life.

The fall time of the current during turn OFF is also critical, as it produces voltage spikes (due to the parasites

elements of the board) that increase the voltage drop across the PDMOS.

In order to minimize these problems, a new driving circuit topology has been used and the block diagram is

shown in figure below. The basic idea is to change the current levels used to turn the power switch ON and OFF,

based on the PDMOS and the gate clamp status.

This circuitry allows the power switch to be turned OFF and ON quickly and addresses the freewheeling diode

recovery time problem. The gate clamp is necessary to ensure that VGS of the internal switch does not go higher

than VGSmax.

The ON/OFF Control block protects against any cross conduction between the supply line and ground.

Figure 5. Driving circuitry

VCC

VgsMAX

CLAMP

GATE

STOP

DRIVE

DRAIN

ON/OFF

CONTROL

OFF

ON

IOFF

PDMOS

L

OUT

VOUT

ION

D

COUT

ILOAD

5.7

Thermal shutdown

The shutdown block generates a signal that turns OFF the power stage if the temperature of the chip goes higher

than a fixed internal threshold (150 ± 10 °C). The sensing element of the chip is very close to the PDMOS area,

ensuring fast and accurate temperature detection. A hysteresis of approximately 20 °C keeps the device from

turning ON and OFF continuously.

DS5503 - Rev 6

page 9/33

Share Link: