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BQ78350-R1: Request the Design Review.

Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76930, BQ78350, TIDA-01093, BQ34Z100-G1, BQ34110, BQ34Z100, TIDA-010030

Hello

My Customer Designed 20S Cell BMS using BQ78350-R1 & BQ76930.

Could you review for attach design file?

Best Regards.
CH_B_DRIVER.pdfCH_B_CTRL.pdfCH_A_DRIVER.pdfFET_DRIVER.pdfCH_A_CTRL.pdf

  • Hi Louis,

    We will review this as soon as possible, but it will be one or two days since we are just returning from the US holidays. 

    Sorry for the delay,

    Matt

  • Hi Matt

    I will wait your feedback.

    Best regards.

  • Hi Louis,

    I looked through the schematic today and it looks good. It looks like this is based on the 20S TI Reference design except that you are using 2 BQ78350-R1 companion gauges instead of a microcontroller to interface with the BQ76930 devices. 

    I think the one big problem is the top BQ78350-R1 will not have any current measurement information for gauging since the top BQ76930 device does not have a connection to a sense resistor. The top BQ78350-R1 will not be able to report the state of charge and I am not sure if it might cause other issues in the operation.

    Regards,

    Matt

  • Hi Matt

    Thanks for your review.

    We update the Schematic to your recommended specifications.

    Can you review the Schematic One more?

    5722.CH_B_DRIVER.pdf2072.CH_B_CTRL.pdf7607.CH_A_CTRL.pdf3323.CH_A_DRIVER.pdf8304.FET_DRIVER.pdf

    Best regards.

  • Hi Louis,

    I don't think this implementation will work. The voltage difference is going to be too big on the SRP/SRN pins of the top device since they are now connected to GND of the bottom device.

    Regards,

    Matt

  • Hi matt

    thanks.

    How should I connect?

    Please suggest how to connect

    Best regards.
  • Hi Louis,

    I think you would need to have a second sense resistor between cells 15 and 16 for the top device. 

    However, I think this design might become very complicated in operation. I do not think anyone has tried to stack two BQ78350 gauges like this before. Since the upper and lower device do not communicate with each other, it may be very complex to do cell balancing between the top and bottom cells, and the fault handling and gauging might be pretty tricky.

    I think a safer approach would be to follow TIDA-01093 since this has been used successfully in multiple systems. In this reference design, one microcontroller communicates with both BQ76930 devices and is able to make decisions based on the inputs from both devices. If gauging is needed, the BQ34Z100-G1 or BQ34110 are both good options. TIDA-010030 shows an example using the BQ34Z100 in a 13S application - the same idea can be used for this system.

    To summarize, I think 2 x BQ76930 + MCU + BQ34Z100-G1 is the cleaner solution using TIDA-01093 and TIDA-010030.

    Best regards,

    Matt