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TIDA-00792: DSG Mosfets are burning

Fikret Yıldırım
Prodigy 115 points
Part Number: TIDA-00792
Other Parts Discussed in Thread: CSD19536KTT, CSD19536, BQ78350-R1A, BQ78350-R1, BQ76940

Hİ 

I am using tida-00792 referance design schematic , but I need to higer current for load, so I applaying same changing such that I adding 5 parellel charge and discharge mosfets and 5 parellel 3mohm parelle resistor.

When I was connecting 4kw load on bms, calculated need current is 120 amper, for 15s1p fifepo4 .In bq studio  showing ASCD  short circuit  protection and bms turn off dsg fet but my dsg mosfet are burning due to my ascd and ascd delay timm are 8us and ascd treshold are maximum .  In my design using csd19536ktt mosfet . 

  • 0
    TI__Guru 54715 points

    Hi Fikret,

    There are 3 areas to check: First is whether the turn off is effective.  See the considerations in the ap note https://www.ti.com/lit/pdf/slva729 and TIDA-00792.  The beads in the individual gate paths or small resistors avoid FET oscillation at turn off which can burn FETs. The CSD19536 MOSFETs have benefited from the beads in our tests.  Also TIDA-00792 used a 620 ohm DSG to gate resistor with 2 FETs, with more FETs that value may need adjustment. 

    The second thing to check is the BQ78350-R1 recovery conditions.  After ASCD the gauge will attempt to recover until the latch limit is reached. See the BQ78350-R1A technical reference manual section 3.6.2 Short Circuit in Discharge Protection for settings.  Recovery times are in seconds. Leaving the Latch Limit at 0 should cause the ASCD to latch on the first occurrance so the FET does not heat.  Higher counts may allow the FETs to heat with each recovery attempt until after several ASCD events they fail.  

    A third thing to check is the reaction and timing of the SCD.  The BQ76940 architecture requires the power filter to maintain operating voltage during the SCD event timing.  See the application note https://www.ti.com/lit/pdf/slua749 section 3.  The power filter components are large to maintain the supply voltage during SCD.  Shorter delay settings will provide more margin to avoid reaching VSHUT.  If the part reaches VSHUT the time to turn off DSG may be extended several ms.  Of course be sure that the SCD current reaches the SCD threshold or the BQ76940 will not react.