L9659 datasheet(23/51 Pages) STMICROELECTRONICS

23 / 51 page

L9659

Functional description

Doc ID 022048 Rev 2

23/51

Figure 7.

Deployment drivers diagram

Driver activation

The firing of a squib driver requires the appropriate FEN function to be active and two

separate sixteen bit writes be made over the SPI. The FEN function is defined as the result

of the FENx pin OR’d with the internal FENx latch. The FENx pin going high initiates the

FEN function. With the FEN 1 function being active and the appropriate Arm and Fire

commands sent then Squib_0 & 1 drivers would be activated. With the FEN 2 function being

active and the appropriate Arm and Fire commands sent then Squib_2 & 3 drivers would be

activated. With the FEN 3 function being active and the appropriate Arm and Fire

commands sent then Squib_4 & 5 drivers would be activated. With the FEN 4 function being

active and the appropriate Arm and Fire commands sent then Squib_6 & 7 drivers would be

activated.

The first write is to ARM the drivers in preparation of receiving the fire command. The Arm

command will stop on all channels any diagnostics that are active. Any combination of

squibs can be armed. The second write is a FIRE command that must directly follow the

Arm command and will activate the desired driver pairs assuming the FEN function is valid.

If there is a parity mismatch the data bits will be ignored and the squib drivers will not have

their status changed, and the two write sequence must then be started again. If there is a

mismatch in channels selected then only those channels selected in both the Arm and Fire

commands will be activated.

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