L9660 datasheet(23/49 Pages) STMICROELECTRONICS

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L9660

Functional description

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 is 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 L9660

begins 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 are

not activated but the tDEPLOY timer starts. If the FEN function becomes active before

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

does not become active before tDEPLOY has expired then the sequence needs 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 are

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 becomes active. This flag remains

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

function the DEPLOY_STATUS flag is 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 is active

following the completion of the driver activation period. This flag is 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 remains ‘0’.

Once the Deploy Success Flag is set, it inhibits 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 can be

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