L9779WD-SPI datasheet(24/141 Pages) STMICROELECTRONICS

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Functional description

L9779WD-SPI

24/141

DocID027721 Rev 2

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.

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.

Figure 8. Power-down sequence without power latch mode

L9779WD-SPI Datasheet(PDF) 24 Page - STMicroelectronics