L9679P datasheet(206/272 Pages) STMICROELECTRONICS

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Safing logic

L9679P

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DocID029275 Rev 1

A specific waveform needs to be present on ACL input in order to instruct L9679P to arm all

deployment loops. L9679P is designed to support the Additional Communication Line (ACL)

aspect of the ISO-26021 standard, which requires an independent hardwired signal (ACL) to

implement the scrapping feature. The disposal signal may come from either the vehicle's

service connector, or the systems main microcontroller, depending on the end customer's

requirements.

The arming function monitors the disposal PWM input (ACL pin) for a command to arm all

loops for vehicle end-of-life airbag disposal. The disposal signal characteristic is shown in

Figure 64. To remain in Arming state, at least three cycles of the ACL signal must be

qualified (in addition to the periodic KEY value being received from the microcontroller). For

the device to qualify the periodic ACL signal, the period and duty cycle are checked. Two

consecutive cycles of invalid disposal signal are to be received to disqualify the ACL signal.

If the logic detects that the signal is incorrect or missing while in Scrap state, the device will

stay in Scrap state; would it happen in Arming state, it will transition to Scrap state

immediately.

Figure 64. Disposal PWM signal

The disposal PWM signal cycle time and on time parameters can be found in the electrical

parameters tables.

L9679P 数据表(PDF) 206 Page - STMicroelectronics