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Original question:

TIDA-010208: Optimizing resistor selection for PACK and LD sensing

TIDA-010208: BMS Buck Convertor Power Source

Steven Shenker
Intellectual 800 points
Part Number: TIDA-010208
Other Parts Discussed in Thread: LM5163,

Hi there,

I have two questions I hope you can help me with.

1. I noticed for this design the LM5163 Buck is powered off of Cell16+ and not after the fuse. This implies that if there were a short circuit/overload fault with the Buck the fuse would not open and current would continue to flow via the Cell16+ balance connector. Is there any reason for this or was this unintended? 

2. I see some redundancy with D47 and the reverse charge circuit of Q29+surrounding components. Is the reverse charge circuit necessary if we have D47? It looks like it would only come into play if D47 were to fail? 

Thanks in advance,

Steve 

  • 0
    TI__Expert 3145 points

    Hi Steve, 

    Please refer below comments: 

    1. I noticed for this design the LM5163 Buck is powered off of Cell16+ and not after the fuse. This implies that if there were a short circuit/overload fault with the Buck the fuse would not open and current would continue to flow via the Cell16+ balance connector. Is there any reason for this or was this unintended? 

    Ryan: LM5163 has internal current limit function which can guarantee the output current below 0.75A typically (https://www.ti.com/lit/ds/symlink/lm5163.pdf?ts=1631063616165&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLM5163), since TIDA-010208 uses a 30A fuse, LM5163 output short circuit won't blow the fuse. Further more, if LM5163 output is shorted, MCU will power off and pull low EN of LM5163, this will disable LM5163. 

    2. I see some redundancy with D47 and the reverse charge circuit of Q29+surrounding components. Is the reverse charge circuit necessary if we have D47? It looks like it would only come into play if D47 were to fail? 

    Ryan: When a charger is attached reversely, because of the big output e-cap of the charger, there will be a huge current flowing through D47 and generate a big voltage to turn on DSG MOSFET, this is a risk. Another scenario is when turning off DSG MOSFET with SCD, D47 will carry on a huge forward current, otherwise the di/dt will generate a huge voltage which will damage DSG MOSFET. 

    Please click "This resolved my issue" if no more questions. Thanks.

    Best Regards,

    Ryan Tan

  • 0 in reply to Ryan Tan
    Intellectual 800 points

    Hi Ryan, 

    Thanks for your answer. That make sense. Regarding 2, I am still not clear. If D47 is there for those reasons, then why do we need Q29 reverse charge circuit? Is this not redundancy?

  • +1 in reply to Steven Shenker
    TI__Expert 3145 points

    Hi Steven,

    Even with D47, PACK+ side still have risk of big enough minus voltage (SCD, reverse charger) and turn on DSG MOSFET, so Q29 related circuit and D47 are both required.

    Thanks. 

    Please click "This resolved my issue" if no more questions. Thanks.

    Best Regards,

    Ryan Tan

  • 0 in reply to Ryan Tan
    Intellectual 800 points

    Thank you for your help