bq29311 question

Carl Wolfe

Other Parts Discussed in Thread: BQ2085-V1P3, BQ29311

submitting following question for review and response:

bq29311/bq2085-v1p3 ESD Immunity Problem

For a bq29311, what is the timing relationship between an over current, brownout or short circuit fault being detected, the programmed delay times, XALERT and the turnoff times for CHG and DSG FET drives? Should I expect just prop delay times for some of this or does everything get clocked at 32KHz? I can see XALERT go low about 1us after I do an ESD discharge to the system. Is this because the bq29311 is asserting XALERT because it detected a fault or is the discharge itself setting XALERT?

over 11 years ago

0 Chris DeWitt over 11 years ago

Prodigy 90 points

Does anyone (Including people from TI) understand how signals like XALERT and the DSG, CSG FET drivers are driven inside the 29311? Are they driven directly by ouputs from comparitors or are they clocked by the 32KHz clock? If so how can they change in 1uS or less?

0 ThomasCosby over 11 years ago in reply to Chris DeWitt

TI__Guru 73830 points

Chris

The CHG, DSG and XALERT resgisters are clocked using the 32 KHz clock, so there will be a delay when turning them on and off during normal operation. The registers are bypassed in the event that a safety fault occurs and the FETs are turned off immediately.

Regards
Tom

0 Chris DeWitt over 11 years ago in reply to ThomasCosby

Prodigy 90 points

Tom -

Thank you. What is the prop delay from something like a short circuit happening to a FET being shut off?

0 ThomasCosby over 11 years ago in reply to Chris DeWitt

TI__Guru 73830 points

Chris

I measured the FET turn off time to be about 500us.

Tom

0 Chris DeWitt over 11 years ago in reply to ThomasCosby

Prodigy 90 points

was Tom -

We have measured some events during an ESD discharge and found that the bq29311 DSG output turned off in about 150nS and the XALERT signal was active in less than 1uS.

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bq29311 question