L9779WD datasheet(25/170 Pages) STMICROELECTRONICS

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L9779WD

Functional description

169

An additional feature for the starter delay drivers is that the starters are only shut-off after

the time delay THOLD if the SEO condition is still active. To satisfy the Secure Engine

Switch off THOLD time, we need to activate the drivers OUT1-4 at least for 225 ms and the

OUT 13/14 at least for 600 ms when the Key is ON, the Watch DOG Algorithm [Watchdog

influence Section 6.17.2] is served and the PWL is enabled after the power on.

The KEY_ON, WDA and “OUT 13/ 14 Switch ON” events for 13 and 14 channels or the

KEY_ON, WDA [Watchdog influence Section 6.17.2] and "OUT_1-4 Switch ON" events for

1 to 4 channels are “anded” by the internal SEO filter in order to guarantee the THOLD

switch off time after the KEY OFF. Example: If the Key is not maintained in ON state for at

least 225 ms for driver 1 to 4 and 600 ms for drivers 13/14, the SEO hold time will not be

granted and the drivers are switched off immediately at next Key turn OFF. The same

behaviour will happen if the WDA [Watchdog influence Section 6.17.2] is not served

(EC ≥ 4) for 225 ms and 600ms when Key is in ON state after the POWER ON.

The ignition stages are not affected by the SEO signal. This is different from the WDA signal

which additionally switches off the ignition stages.

To avoid misunderstandings one must be aware that the SEO function has nothing to do

with the WDA function and is not a part of the WDA module. The SEO function is related to

the key switch, not to the WDA function. The SEO function adds an additional safety

procedure for switching off.

Other functions than the injector stages and the starter relay drivers are not affected or

influenced by the SEO signal.

With the falling edge of KEY_ON a timer is started which disables the mentioned power

stages after 200 ms to 250 ms (typ. 225 ms). The timer is clocked by an internal oscillator.

The timer does not depend on any µC clock or function. The µC still has control on switching

on/off drivers during SEO time. This function is configured by CONFIG_REG6 register. After

a SEO event, KEY should be stay ON for at least 600ms so to allow a further SEO event

delay.

L9779WD 데이터시트(PDF) 25 Page - STMicroelectronics