L9680 datasheet(206/277 Pages) STMICROELECTRONICS

206 / 277 page

Safing logic

L9680

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POS_COUNT and NEG_COUNT are not updated if microcontroller stops reading SAF_CC

bits (this must be avoided otherwise ARMING set and reset will not be possible).

By way of the assignment of the ADD_VAL, SUB_VAL, ARMP_TH and ARMN_TH settings,

the safing engine can be configured to assert arming for either a simple accumulation of

COUNTs in a non-consecutive manner, or it could be set to require some number of

consecutive samples.

12.5

Safing engine output logic (ARMxINT)

SPI messages are monitored and mapped to specific safing records. Each safing record is

configured with its own threshold, dwell time and the appropriate ARMxINT signal to

activate if safing criteria are met.

Any enabled safing record can be programmed to an arming signal. All safing records

arming status is logically ‘OR'd’ to its programmed arming signal. For example, if safing

records 1, 2, 4 are programmed to ARMINT1 and the records are enabled, any of the

records can set the ARMINT1 signal. Configuration of safing record mapping to ARMxINT

signals is specified in the in the SAF_CONTROL_x register (refer to Table 67).

While in Diag state, L9680 allows diagnostics of the squib driver HS and LS FETs, ARM

pins, VSF output and firing timers. The ARM and VSF output tests are mutually exclusive.

For safety purposes, the safing logic circuitry is physically separated from the circuitry that

contains the deployment logic.

L9680 Datasheet(PDF) 206 Page - STMicroelectronics