BQ76940: damage

kevin.huang_FJXM

Part Number: BQ76940
Other Parts Discussed in Thread: STRIKE,

HI Teams:

BQ7694003DBTR chip is used for 15-circuit single cell voltage sampling. It is easy to be damaged under the following two conditions. Please help to see what causes it, thank you!

Question:

Condition 1: BQ7694003DBTR is used for 15-circuit single cell voltage sampling. The connector connected to the cell voltage sampling is easy to be damaged. When damaged, the 15th or 14th circuit cell sampling is 0.046V (actual voltage 3.3V),

The sampling is normal after replacing the BMS chip. There are 6 damaged boards;

Working condition 2: use electric soldering iron to weld the test point 3.3V of the peripheral circuit of BMS chip_ REF and 0V_ D. After welding, power on again. It is found that the 14th circuit core sample is 0.046V (the actual voltage is 3.3V);

over 2 years ago

0 Luis H. S. over 2 years ago

TI__Mastermind 42060 points

Hello Kevin,

You mention that the connector is easily damaged, does this mean that the IC gets damaged after attaching the cells? Are you attempting to hot-plug the batteries or is this during initial assembly?

Are ESD considerations being taking into account? I find it odd that it would get damaged during welding. But if an ESD strike were to happen, it could potentially damage the IC.

On an unrelated note, I notice that you are using a BJT for cell balancing, due to the internal cell balancing limitations of the BQ76940, using BJTs may not be a great option. Have you tested the cell balancing circuit and see if it meets your requirements? Typically we recommend to use FETs for external cell balancing when using the BQ76940. This E2E thread briefly explains this: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/907783/bq76940-balancing-with-transistor

I also notice that the resistors next to C147 and C143 are too small. Typically we recommend a 1-kOhm resistor for both of these. There may be issues if kept at 100-Ohm.

Best Regards,

Luis Hernandez Salomon

0 kevin.huang_FJXM over 2 years ago in reply to Luis H. S.

Expert 2925 points

hi Luis :

Help confirm whether the wiring sequence is affected.

Our current wiring sequence is as follows:

Connect B - (0V_D), connect VC0~VC8, connect VC9~VC15, connect B+, and turn on BMS board power

0 Luis H. S. over 2 years ago in reply to kevin.huang_FJXM

TI__Mastermind 42060 points

Hello Kevin,

That sounds correct with me. You connect from the bottom to the top, like you are doing. Section 10 Random Cell Connection – Within Limits of the bq769x0 Family Top 10 Design Considerations talks about all the considerations that must be taken when connecting the cells.

Best Regards,

Luis Hernandez Salomon

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BQ76940: damage