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BQ76930: Power management forum

Sophia Yao
Prodigy 701 points
Part Number: BQ76930
Other Parts Discussed in Thread: TIDA-01093,

Hi,

could you please help to review below schematic. the application is 20s battery solution. if you need the details, i can send email to you.

thanks and best regards,

Sophia

  • 0
    TI__Guru 54715 points

    Hi Sophia,

    Of course the video https://training.ti.com/how-create-schematic-bq76920-bq76930-and-bq76940 may be helpful, as would the TIDA-01093.  Observations:

    • The input filter capacitors C1, C2, etc are 1 uF, this is the value shown in the EVM , it can show voltage artifacts while balancing if balancing is used. Smaller capacitors such as 0.22uF are sometimes used with balancing.
    • C31 and C32 should normally be the same value as the other input filter capacitors
    • Be aware of the situation shown in figure 21 of http://www.ti.com/lit/pdf/slua749  when your J2 and J5 mate and add zener diodes if this is a concern in your application for the VC5B and  VC6 inputs.
    • The connection of R51, at Q23 gate is like TIDA-01093 and should work similarly. You might consider if pullup of R58 to VCC_U is OK in your circuit.
    • Be sure your FETs work well in parallel without individual gate resistance.  Some FETs may oscillate without a damping resistance, consult your FET supplier.

    If you have followed TIDA-01093 the board should work like that design.

  • 0 in reply to WM5295
    TI__Prodigy 701 points

    Hi,

    thanks for your timely reply. Yes, the design followed TIDA01093, and I have send the whole schematic to your email. Does the schematic have any problems?

    thanks and best regards,

    Sophia

  • 0 in reply to Sophia Yao
    TI__Guru 54715 points

    Hi Sophia,

    The TIDA-01093 was built and tested as described in the design guide, it does not have known problems.  There are design choices however such as the R58 note mentioned above.  It is not a problem, just an option. 

    Additionally the turn off circuit for the power FETs uses the SCR-like circuit described.  Some designers are not comfortable with this since if it is triggered by transients the DSG will turn it back on again.  There was an e2e question recently on this where the circuit was implemented differently. The customer schematic follows the TIDA-01093 well, so it should work similarly in this aspect also, the performance with a different type and more FETs of a different type will need tested of course.

  • 0 in reply to WM5295
    TI__Prodigy 701 points

    Hi,

    Got it. Another question, as the datasheet shown, the BQ76930 can achieve load detection function while DSG and CHG MOS are disabled(by detecting CHG pin voltage). if the design need 2 pieces of BQ76930(just like TIDA01093 shown), how to design load detection when BQ76930 is in SHIP mode?

    thanks and best regards,

    Sophia

  • 0 in reply to Sophia Yao
    TI__Guru 54715 points

    Hi Sophia,

    The CHG pins from the BQ76930 in TIDA-01093 and the customer design go to gates of transistors, so there is not a path to pull up the CHG pin to detect load.  The TIDA-01093 design guide discusses load detect and charger detect circuits and has sections for test results.  The customer seems to have duplicated these circuits.

    When the BQ76930 is in ship mode power is off, in both cases the MCU is powered by a BQ76930, so there would be no processor for decision making.  The processor could be powered by a separate regulator so it could make decisions on when to boot the BQ76930s based on its signal detection.  Alternatively some analog circuit could be developed to boot the BQ76930s based on a different signal condition than the current charger detection.  It would be unique design for your specific customer requirements.