L9659 datasheet(24/51 Pages) STMICROELECTRONICS

24 / 51 page

Functional description

L9659

24/51

Doc ID 022048 Rev 2

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 for driver

activation. If a command is between the ARM and FIRE command then the sequence must

be restarted. An error response will 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 L9659

will 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 will 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.

Figure 8.

Driver activation timing diagram

Only the channels selected in the ARM and, directly following, the FIRE command will be

able to be activated.

By reading the appropriate registers a status of the deployment is provided. If a valid

Arm/Fire sequence has been provided the status flag will become active. This flag will

remain active for as long as the TDEPLOY timer is counting. Depending on the state of the

FEN function the DEPLOY_STATUS flag will be active a minimum of TDEPLOY and a

maximum of 2 x TDEPLOY. If driver activation did occur (both a valid Arm/Fire sequence and

the appropriate FEN function active within the appropriate time) then the

DEPLOY_SUCCESS flag will be active following the completion of the driver activation

period. This flag will be active until cleared by software. If a valid Arm/Fire sequence did

occur but the FEN function was never activated within the TDEPLOY time then the

DEPLOY_SUCCESS flag will remain ‘0’.

Once the Deploy Success Flag is set, it will inhibit the subsequent deployment command

until a SPI command to clear this deployment success flag is received. Bits D7 through bit

D0 are used to clear/keep the deploy success flag. When these bits are set to ‘1,’ the flag

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