L9662 datasheet(31/80 Pages) STMICROELECTRONICS

31 / 80 page

DocID028325 Rev 1

31/80

L9662

Functional description

The ASIC shall be protected against inadvertent turn on of the firing drivers unless the

appropriate conditions are present. Non-typical conditions shall not cause driver activation.

This includes the case where VRESx and/or VSDIAG pins are connected to a supply up to

40V and VDD is between 0V and VDD min. Under these conditions the device shall ensure

that driver activation will not occur. No flow of current shall be allowed through the SQHx

and SQLx pins.

Driver activation

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

separate sixteen bit writes to be made over the SPI1. 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_1 & 2 drivers would be activated. With the FEN 2 function being

active and the appropriate Arm and Fire commands sent then Squib_3 & 4 drivers would be

activated.

With the FEN 3 function being active and the appropriate Arm and Fire commands sent then

Squib_5 & 6 drivers would be activated. With the FEN 4 function being active and the

appropriate Arm and Fire commands sent then Squib_7 & 8 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 to actually activate the desired driver pairs. 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.

During the first write, when the drivers are armed, all diagnostic functions are cleared. The

FIRE command must follow the ARM command along with the FEN function active in order

for driver activation. If a command is between the ARM and FIRE command then the

sequence must be restarted. An error response shall be received for the Fire command if

the ARM/FIRE sequence is not followed.

The ARM/FIRE commands and FEN function are independent from each other. The device

shall begin the tDEPLOY timer once a valid ARM/FIRE sequence has been received. If a valid

ARM/FIRE command has been sent and the FEN function is inactive then the drivers will

not be activated but the tDEPLOY timer shall start. If the FEN function becomes active before

tDEPLOY has expired then the drivers will become active for the full tDEPLOY time. If the FEN

does not become active before tDEPLOY has expired then the sequence would need to be

restarted. A diagram illustrating this is shown in Figure 8

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