BQ76952: BQ76952: Effect of AFE sampling accuracy during balancing

Star Xu

Part Number: BQ76952

I have a query need your help.

By configuring the software to open odd or even cell balancing, it has an impact on the sampling error of other sections (see the figure below for detailed data), and not only on cell15. Therefore, during balancing, the sampling accuracy cannot be compensated only for cell15 (n * 35 uA* 100Ω/1000=3.5（mV） * n). What is the reason for the impact on the sampling accuracy of other cells? Is it inconsistent with the description in the specification? How to avoid the impact of sampling errors on other cells?

1，To open odd cell balancing，and then cell5、cell7、cell9、cell11、cell13、cell15 sampling accuracy is affected.

2，To open even cell balancing，and then cell6、cell8、cell10、cell12、cell14 sampling accuracy is affected.

Waiting for your reply.

Thanks

Star

over 1 year ago

0 Jose Couso over 1 year ago

TI__Mastermind 23091 points

Hello Star,

Can you please measure the voltage at the input of the cells and also measure the voltage at the pins of the AFE? It'd be good to log this voltage measurements and see if they differ while cell balancing.

The only thing I think might be affecting the cell measurements during cell balancing are the Zener diodes across the input pins. These Zeners are rated 7.5V, and the cell voltages could go as high as the 7.5V turning ON the diodes and causing voltage to drop. It'd be good to remove the Zeners and see if it fixes the issue.

Regards,
Jose Couso

+1 Jose Couso over 1 year ago

TI__Mastermind 23091 points

Hello Star,

I was discussing with my team, and turns out the BQ76952 has Measurement Disturbance During COV/CUV Checks. This is more detailed discussed in section 2.5 from the cell balancing app note.

Also, to help with the voltage readings, smaller RC filter could be used in the input cell pins.

A workaround on this would be to ignore 2 measurements out of three while balancing.

Regards,
Jose Couso

0 Hugh Yang over 1 year ago in reply to Jose Couso

TI__Intellectual 780 points

Hi Jose,

This is my customer's case. This sch. is the previous one. In the new design, they replace the Zener diode between inputs by capacitor to GND. Any affects by this capacitor?
The RC in customer's design, 100Omega/ 220nF is same to our demo.

Br,

Hugh

0 Jose Couso over 1 year ago in reply to Hugh Yang

TI__Mastermind 23091 points

Hello Hugh,

Please post the question in a new thread. This is simply to better keep track of threads and not discuss multiple topics.

Please include the schematic in the new thread.

Regards,
Jose Couso

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BQ76952: BQ76952: Effect of AFE sampling accuracy during balancing