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BQ76952: SCD not functioning

Nico Ferreira
Prodigy 30 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Good Day  .

We are testing the SCD on our high current  system  ( 16 s / 300A )  

Shunt is a 300 A 75 mV .  Normal current measurement and all other functions of the BMC chip are working fine  .

For testing basic  SCD action we set the trip level to   " 0  "   10 mV over the shunt      value  .     We expect the SCD  to be detected once we pass  10mV -  

We ramp up the current by selecting loads ,   4mV - all good   8mV all good    12 mV  SCD trip   -  and if we remove the load it will reset itself after about 5 sec .  NO problem  .

We can ramp the current up to increase the shunt voltage well above 10 mV and it works fine (the trip action  )  -  but only on one board of 3  battery packs that are connected in parallel  .  

3 identical battery packs  - each with its own bms unit and shunt  .  Only the one bms chip /board will detect the set SCD limit and react on it  .

All 3 have the exact same settings programed , same circuit  .   Even when we test the battery packs on their own  - 2 of the 3 will not react to a SCD limit event  .

We unplugged all cables to the pcb  - total power cycle  ,  verified the set values in the BMS chip  ( write to an read out of BMS chip  to verify ) but no improvement.

Chip is not in TEST mode  .

Any idea why 2 out of 3 will not work as expected  ?

 Kind regards

Nico

  • 0
    TI__Expert 4320 points

    Hello Nico,

    How are you programing the device? Are you using BQStudio?

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Prodigy 30 points

    Hi Thomas  .

    Thanks for your reply. 

    We do a otp with a few setup parameters with BQ studio ,  but for testing we overwrite  some of it in ram     (after power up )  to enable lower current trip testing for example  .    OTP is done only once .

    So we use BQ studio for  OTP  and general  testing -  and also write and read direct from the STM  cpu  as required  .

    Strange part is that we write and verify each parameter  to make sure it is updated in the BMS chip  - and we can read all the other parameters from the chip - so it is working normally   -  it will just not  perform the SCD alert and trip action - discharge pin stays active - flag bit(s)  not set  .

    Strange part is just that the one chip works 100 % but the other not  .

    Kind regards

    Nico

  • 0 in reply to Nico Ferreira
    TI__Expert 4320 points

    Hi Nico,

    Can you send a waveform of the voltage across the sense resistor when you expect a SCD event to occur? 

    Can you also send you schematic?

    Best regards,

    Thomas Rainey