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BQ76940: bq7694001 release from short circuit

Alexander Burtakov
Intellectual 750 points
Part Number: BQ76940
Other Parts Discussed in Thread: TIDA-00792

Hello to Ti support team ,

   I have question according to  problems with schematics based on TIDA-00792 . ( I use long time this schematic without problems first time I have problem like that )

I have some amount of  new batteries 13S1P  that operates different --> After short circuit (~80A)  bq7694001 doesn't disconnects FETS , bq7694001 enters to shut down mode due to absence of power and after ~12msec Fets disconnects (due to shut down state) . IC on shut down  no 2.5V Power and no communication and only charge wake up the IC .  IC proper operates Fets off ~400usec if Load current is lower ~50A and less and IC continue operating .

B.R

Alex.B

     

  • 0
    TI__Guru 54715 points

    Hi Alex,

    It sounds like in some designs you have the part pulling into VSHUT region of power.  The part then loses power and can not shut off the FETs.  Your design must keep VC5X above VSHUT during the short circuit event.  See http://www.ti.com/lit/pdf/slua749 section 3 for a description of the architecture and explanation of the discharge.  Generally keep the filter resistors at 1k, keep the Cf power filter capacitors at 10 uF.  If necessary use a shorter short circuit delay.   It may be that with a higher current there is a lower voltage on the battery during the short and the VC5X discharges more.

  • 0 in reply to WM5295
    Intellectual 750 points

    Thank you for your quick response ,

              According to data sheet http://www.ti.com/lit/ds/symlink/bq76940.pdf Cf_max value can be up to 40uF , Can it  damage in other place if I"ll change from 10uF to 40 uF .  Can I change Cf only on Vc5X ?

    B.R

         

  • 0 in reply to Alexander Burtakov
    TI__Guru 54715 points

    Hi Alex,

    40 uF is unusual but is allowed.  Having 40 uF for VC5X to VSS only would certainly help the VC5X voltage during short circuit since this is the cap with the highest load, it would also skew the voltage during connection.  I don't have experience with such condition.  If you use this technique you may need to control the connection sequence more carefully.