L9679P datasheet(159/272 Pages) STMICROELECTRONICS

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L9679P

Deployment drivers

271

active according to the Arming Enable Pulse Stretch Timer or the ARMx enabling state. The

Arming Enable Pulse Stretch Timers is available in the AEPSTS register.

8.1.4

Deployment current monitoring

A current comparator is used to indicate when the output current from the HSD, SFx,

exceeds the deployment current threshold, ITHDEPL. The timer signal remains active and

increments while the current meets the programmed deploy current as set in the Deploy

Configuration Register. The deploy current counter value is stored in the Deploy Current

Monitor Timer Register XY (DCMTSxy). There is a unique timer register for each channel.

If the deploy current falls below the specified current threshold momentarily and recovers,

the deploy current counter will pause during the drop-out and continue once the current

exceeds the threshold. The deploy current counter will not be reset by the presence or

absence of current in the deployment channel.

Figure 32. Current monitor counter behavior

The deploy current counter is reset to $0000 as soon as a toggle on DEP_DISABLED is

performed and a new DEPCOM command on the same channel is received.

8.1.5

Deployment success

Deploy success flag is set when the deploy timer elapses. This bit (CHxDS) is contained in

the Deploy Status Register. Within the Global Status Word register (GSW), a single bit

(DEPOK) is also set once any of the 12 deployment channels sets a deploy success flag.

8.2

Energy reserve - deployment voltage

One deployment voltage source pin is used for adjacent channels (e.g. SS23 for channels 2

and 3). These pins are directly connected to the high side drivers for each channel.

8.3

Deployment ground return

L9679P is hosted in a particular frame allowing squib driver ground feedback to be

connected to an internal ground ring. This ring is electrically connected to the package

exposed pad and to the GNDSUB1 and GNDSUB2 pins. Connection to these two pins is

made by means of a strong metal layer, therefore this connection is sufficient for all

deployments occurring simultaneously, even in case of only one out of the three possible

connections being available.

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