L9965P datasheet(36/104 Pages) STMICROELECTRONICS

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3.6.2.5

Safe operating area

There is no constraint on the selection between different IDEPLOY_XX and tDEPLOY, so it is under user's

responsibility to prevent excessive thermal heating in the squib driver section by setting the deploy parameters

carefully.

The power stage has been sized according to the following recommended combinations:

•

IDEPLOY_00 and tDEPLOY = 1050 µs

Profile valid for 8.4 V ≤ VPS ≤ 27.3 V (VPS,min = 8.4 V considering max resistance contribute)

•

IDEPLOY_01 and tDEPLOY = 750 µs

Profile valid for 9.8 V ≤ VPS ≤ 27.3 V (VPS,min = 9.8 V considering max resistance contribute)

•

IDEPLOY_10 and tDEPLOY = 550 µs

Profile valid for 11.2 V ≤ VPS ≤ 27.3 V (VPS,min = 11.2 V considering max resistance contribute)

•

IDEPLOY_11 and tDEPLOY = 250 µs

Profile valid for 19.6 V ≤ VPS ≤ 27.3 V (VPS,min = 19.6 V considering max resistance contribute)

The power stage is not sized to stand a deployment event with PF pin shorted to ground. So, if this scenario is

expected, the maximum operating voltage on PS pin should be reduced accordingly to chosen deployment profile:

•

IDEPLOY_00 and tDEPLOY = 1050 µs

This profile is valid for 6 V ≤ VPS ≤ 23 V

•

IDEPLOY_01 and tDEPLOY = 750 µs

This profile is valid for 6 V ≤ VPS ≤ 23 V

•

IDEPLOY_10 and tDEPLOY = 550 µs

This profile is valid for 6 V ≤ VPS ≤ 22 V

•

IDEPLOY_11 and tDEPLOY = 250 µs

Not tolerated

The effective deployment time tDEP_EFF (time interval in which the deployment current value is above 90% of the

programmed target value IDEPLOY_xx) can be calculated as follows:

tDEP_EFF=tDEPLOY−tDEP_DLY=DEP_TIME_x×tDEPLOY_RES−tDEP_DLY

(2)

Where:

•

DEP_TIME_x * tDEPLOY_RES is the equivalent time of the programmed deployment duration counter value.

•

tDEP_DLY is the delay time between the actual receiving of the deployment start signal (SPI CS rising edge

or FENH and FENL acknowledge) and the rising deployment current value reaching 90% of the

programmed target value.

3.6.2.6

Deployment auto-retry

The IC offers the possibility of performing multiple fire attempts in case the first one fails:

•

The HS_RET_CFG bit field configures the maximum number of deployment attempts.

•

The HS_RET_DLY_CFG bit field configures the interval between consecutive retry attempts.

If one of the following conditions occurs, the auto-retry is stopped:

•

FIRE_GOOD is set following a successful deployment.

•

The maximum number of attempts (configured by HS_RET_CFG bit field) is exceeded without a successful

deployment.

The FIRE_GOOD_SEL = 11 case is useful in test case scenario where the Pyro igniter is replaced by a dummy

load: multiple deployments are performed and their number is limited by the configured maximum number of

retries.

Note:

The time between two retries is the bigger between the resistance measurement time and the interval time

defined by HS_RET_DLY_CFG bit field in NVM.

If, once reached the maximum number of attempts, the deployment condition is still present (FENH and FENL

signals still in active state), another retry routine is performed after a minimum delay time of tRET_ROUTINE_DLY.

The number of performed deployments is readable in the DEPLOY_CNT bit field in the DEPLOY_STATUS

L9965P

Functional description

DS14702 - Rev 4

page 36/104

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