L9965P datasheet(35/104 Pages) STMICROELECTRONICS

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The HS switch has been designed to withstand a maximum deployment energy of EHS_DEPLOY_x starting from the

maximum operating TJ.

3.6.2.4

Deployment routine

As soon as the IC enters the ARM state, any ongoing diagnostic is interrupted.

Once in ARM state, if a valid trigger command is received, the tDEPLOY deployment timer starts. The current

flowing in the HS is monitored by a dedicated current comparator, whose threshold is IDEP_MON_TH and is

proportional to the programmed deployment current value IDEPLOY_xx.

One digital current counter is present to count how much time the deployment current stays above IDEP_MON_TH.

It is initialized to 0 upon system power-on and reset. The value is stored in the DEP_CURR_MON bit field located

in the DEPLOY_CURRENT_MONITOR register. The counter is reset when the device goes in ARM state and a

new valid deployment command sequence is received. The value of this counter is then compared with the digital

value of tDEP_MON_TH threshold.

The deployment current monitor timer threshold tDEP_MON_TH can be calculated as follows:

tDEP_MON_TH=DEP

_MON_THR×tDEP_MON_TH_RES

(1)

After a deployment event, a pyro igniter resistance measurement can be performed and the result, saved in the

RES_MEAS_POST register, is compared with the RPYRO_POST_TH threshold selected through VRES_POST_TH

bit in NVM.

Note:

If a deployment attempt ends successfully, the pyro-fuse resistance increases to values greater than 100 Ω.

Hence, if further deployments are attempted, almost the entire PS voltage would fall on the initiator resistance,

which in turn would result in the PF-PR voltage measurement close to saturation. This can be seen as a further

confirmation of the fire outcome (FIRE_GOOD bit set).

The deployment routine ends when the FIRE_GOOD signal is set to 1. In this case the deployment info is saved

and then the device returns in NORMAL state.

Through the FIRE_GOOD_SEL bit field, it is possible to select when the fire good signal is set (Figure 17):

•

Measured resistance value above resistance threshold (FIRE_GOOD_SEL = 00)

•

Deployment current value above the current monitor threshold for the selected deployment current duration

(FIRE_GOOD_SEL = 01)

•

Measured resistance value above resistance threshold AND deployment current value above current

monitor threshold for the selected deployment current duration (FIRE_GOOD_SEL = 10)

•

Fire good signal is never set (FIRE_GOOD_SEL = 11)

Figure 17. Fire good signal selection

RPYRO>RPYRO_POST_x

IDEPLOY>IDEP_MON_TH for tDEPLOY>tDEP_MON_TH

RPYRO>RPYRO_POST_x & IDEPLOY>IDEP_MON_TH for tDEPLOY>tDEP_MON_TH

FIRE_GOOD

FIRE_GOOD_SEL

The “fire inhibit” signal inhibits the deployment of the pyro-fuse, sets the FIRE_INHIBIT latch and asserts the

FAULTN line. Any further deployment is not possible until latched bit is read (clear-on-read bit).

L9965P

Functional description

DS14702 - Rev 4

page 35/104

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