Clarification on Differences Between MC33772B and MC33772C for BMS Integration with S32K144

[sondt308]

Dear NXP Support Team,

I am currently working on a Battery Management System (BMS) using the S32K144 microcontroller and would like to better understand the differences between the MC33772B and MC33772C when integrated into such a system. Specifically, I have the following questions:

1. What are the main differences between the MC33772B and MC33772C in terms of measurement and monitoring capabilities when connected to the S32K144 via SPI communication?
   Are there any changes in the communication protocol or performance?

2. In terms of battery protection features (over-temperature, over-current, over-voltage, etc.), what improvements does the MC33772C offer compared to the MC33772B?
   How do these changes impact the integration and operation with the S32K144?

3. Is the MC33772C backward compatible with existing configurations using the MC33772B on the S32K144?
   Does upgrading from MC33772B to MC33772C require significant software or hardware changes?

4. How do the differences in accuracy for voltage, current, and temperature measurements between the MC33772B and MC33772C impact battery control and protection in the BMS?

I appreciate your assistance and look forward to your response to help guide my component selection for the project.

Best regards,
Son Thai

[TomasVaverka]

Dear Mr. Thai,

There is an application note describing the difference between the B and C version. It is targeting the MC33771, but is valid also for the MC33772. 

AN12633 - Switching from MC33771B to MC33771C:
https://www.nxp.com/docs/en/application-note/AN12633.pdf

BRs, Tomas

[sondt308]

Hello @TomasVaverka,

Thank you for your continued support. I have a few questions related to the Cell Balancing functionality in the BMS system using MC33772:

1. Cell Balancing Time Formula:

   I am using the following formula to calculate the cell balancing time:

   Balancing time = (ΔV * C_rate) / I_bal​​

   Where:

   • ΔV: maximum voltage deviation between cells
   • C_rate: nominal capacity of the battery (Ah)
   • I_bal: balancing current (A)

   Could you please confirm if this formula is correct? If not, could you provide the accurate formula?

2. Actual Balancing Time:

   When applying the formula above with practical values (for example: ΔV = 50mV, C_rate = 32Ah, I_bal = 0.1A), the balancing time comes out to be 16 hours. This seems very long compared to the balancing time mentioned in the datasheet (ranging from 0.5ms to 511ms).

   I am concerned that if the balancing time is this long during an over-voltage situation, would it still ensure safety for the battery and the users? Please help clarify this issue.

3. Reading voltage and current during balancing:

   During the Cell Balancing process, is it possible to continue reading the voltage and current values of the battery? Some references suggest this might lead to inaccurate readings due to the influence of balancing current. Could you please confirm this?

I would greatly appreciate NXP’s support on the above questions.

Best regards,
Son Thai