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BQ77915: Design Not Working: FET's not working

Part Number: BQ77915


I am designing a 10S BMS using 2 BQ77915. I have followed the application notes and Datasheet to design the board. But, the CHG/DCHG Mosfets are not turning ON.

Test Bench: I am using Resistor Divider circuit to test the BMS. 100 ohm resistors have been connected. On the load side, I have connected 1K ohm resistor.

Few points I have checked:

1. AVDD Voltage is 3.0V on both the IC.

2. The Top IC CHG pin  = 12.5V, DCHG pin: 12.5V

3. TS circuit is also made correctly by adding a 10K Resistor.

Please find the schematics in the attachment below for reference.

Please share your suggestions ASAP. I need to finish this design ASAP.

Thank you

Ritul Shah


  • Hi Ritul,

    I don't recognize a problem from the schematic which would prevent the lower device from turning on the FETs.  

    First be sure IC2 is turning on which it seems you have done in #1.  Check the AVDD voltage at C9, it should be about 3V (see the data sheet).  If not check the PRES signal to be sure it is high, it should connect to the LPWR signal of the upper with 10k not shown on the schematic.

    Check the CTRC and CTRD pins with respect to TOP_GND.  You have checked the top IC CHG and DSG are good in #2, be sure it reaches the CTRC and CTRD of the bottom.

    If the part is on it is likely in some fault.  See table 9-5 for a summary of faults which will turn off FETs: Check the conditions for each fault and stimulate the recovery condition.  For example if the 1k load pulls PACK- to PACK+ and the voltage was brought up slowly and the part requires load removal for for UV release, the part may be in UV mode waiting for LD to fall below the VLDT.  CHG may be on but it may not be apparent since PACK- is pulled up.  In this case you might momentarily short PACK- to BAT- to see if it recovers or apply a charger to bring PACK- low.  This may not be the fault in your situation, see the table and work through the recovery conditions shown.