L9678P datasheet(115/203 Pages) STMICROELECTRONICS

115 / 203 page

DocID029274 Rev 3

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L9678P, L9678P-S

Deployment drivers

202

fast comparator detecting the open condition, the driver is able to discharge the FET gate

quickly in order to reduce current overshoot and prevent potential driver damage when the

short to ground occurs.

6.4.5

Intermittent open squib

A dedicated protection is also available in case of intermittent open load during deployment.

In this case, if load is restored after an open circuit, due to slow reaction of the high-side

current regulation loop, the current through the squib is limited only to ILIMSRx by the low

side driver. If this condition lasts for longer than tLIMOS then the high side is turned off for

tHSOFFOS and then reactivated. By this feature, intermittent open squib and short to battery

faults may be distinguished and handled properly by the drivers.

6.5

Diagnostics

The L9678P provides the following diagnostic feedback for all deployment channels:



High voltage leakage test for oxide isolation check on SFx and SRx



Leakage to battery and ground on both SFx and SRx pins with or without a squib



Loop to loop short diagnostics



Squib resistance measurement with leakage cancellation



High squib resistance with range from 500 Ω to 2000 Ω



SSxy, SFx and VER voltage status



High and low side FET diagnostics



High side driver diagnostics



Loss of ground return diagnostics



High side safing FET diagnostics



Deployment Timer diagnostic

The above diagnostic results are processed through a 10 bit Analog to digital algorithmic

converter. These tests can be addressed in two different ways, with a high level approach or

a low-level one. The main difference between the two approaches is that with the low level

approach the user is allowed to precisely control the diagnostic circuitry, also deciding the

proper timings involved in the different tests. On the other hand, the high level approach is

an automatic way of getting diagnostic results for which an internal state machine is taking

care of instructions and timings.

The following is the block diagram of the squib diagnostics.

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