L9663 datasheet(19/104 Pages) STMICROELECTRONICS

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L9663

Power supply

103

Figure 9. VAS application diagram

When POR is active, the VGS output pin is driven low to keep external N-ch switched off.

The VAS pre-regulator is automatically activated with a soft start at POR and automatically

switched off, after a filter time, if VAS falls below VVASU_off. It can be later controlled off or on

by means of a dedicated VAS_EN bit. To protect the external component from exceeding

maximum allowed gate to source voltage if VAS is shorted to ground by a fault, an internal

passive clamp is implemented on VGS.

The integrated charge pump, supplied by VASSUP, assures proper voltage regulation in

case of low voltage conditions. It is automatically switched off in case the voltage on VASSUP

is high enough to allow proper regulation.

If the pre-regulator is not needed, the VAS_EN bit can be set to '0' to switch off the pre-

regulator itself. The pin VGS can be left open, and the VAS pin directly connected to the

regulated voltage in the ECU.

The pre-regulator is active independently of RESETN input pin if the supply voltage of the

internal analog/digital circuits is available.

2.3

Voltage supply for synchronous pulse generation VSYNCx

To use synchronous PSI5 sensors and for ECU-to-sensor communication, the transceiver

IC needs to generate synchronization pulses. These require a voltage which is higher than

VAS.

This module generates the necessary voltage VSYNCx by two bootstrap circuits. Two

capacitors with two transceiver IC pins each are used as external components of this

module.

The bootstrap blocks start pre-charging the external capacitors after POR (with a 2 ms time

gap between the first and second block).

The bootstrap circuits are enabled by default, activated by internal logic with timing sync

pulses dependent, and can be disabled later on through a dedicated SPI command. The

bootstrap block can recharge the capacitor so that subsequent sync pulses are allowed with

a minimum period of 200 μs.

A useful option is the possibility to connect the BHx pin directly to a high voltage rail. In this

configuration, VB has also to be connected to the same high voltage rail and the bootstrap

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