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L9961 BMS IC Configuration and Debugging Issues

JSleeeee
Associate

My name is Jeongsoo Lee.

 

We are using the L9961 (BMS IC) and have configured the circuit using the L99615C development board to establish a basic framework. However, our battery solution requires a 3-series configuration.

 

The datasheet and development report guide connecting from cell 1, but there is no information on handling the remaining cell 4 and 5 pins.

 

I also have additional questions regarding whether the entire circuit ground should be connected to C0. Our specific questions are: Should the C4 and C5 pins be left floating, or should they be grounded?

Should the entire ground of the BMS IC and MCU be connected based on C0?

 

When debugging our BMS board based on the L99615C circuit (5 cells to 3 cells) using the STSW-L9961BMS code, we are encountering an issue where Cells 1 to 3 are read in reverse order. Is this expected behavior?

 

When applying 3V to Cells 1 to 3 using a cell simulation device, the measured voltage differs from the actual voltage.

 

The voltage across the capacitors of the Cell voltage sensing and balancing circuit differs from the simulated cell voltage values.

 

We are facing multiple complex issues and are finding it difficult to determine whether this is a simple artwork issue or if the improper handling of the unused C4 and C5 pins is causing the malfunction.

 

We look forward to your appropriate response.

 

Thank you for your assistance.

 

Best regards, Jeongsoo Lee

1 REPLY 1
GS98
ST Employee

Dear Jeongsoo,

The unused pins C4 and C5 should be short-circuited to C3 and C3 should be connected to the battery (B+), upstream of the diode on VB pin.

The entire ground of the BMS IC and MCU should be connected to the GND of the battery negative.

Please proceed to connect the unused pins as suggested and then perform another voltage measurement.

If you still experience unexpected behavior, please provide more details and attach a picture of your results - we will help you as best we can.

Best Regards,

GS