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BQ79616-Q1: Request for schematic review (BQ79616 & M0L1304)

Reider McFeely
Prodigy 45 points
Part Number: BQ79616-Q1
Other Parts Discussed in Thread: BQ79616,

Tool/software:

Hi All,

We have a schematic we'd like to have reviewed/get feedback on if at all possible. Mostly wanting to make sure we didn't miss anything obvious before sending it off for a first prototype batch Slight smile.

bms_ver1.3_review.pdf

Specific questions:

- Are external pulldown resistors for BQ79616 unused GPIO necessary, or can internal pulldowns be used?

- TVS diodes necessary for GPIOs used with externally mounted thermistors?

Any feedback is welcome!

  • 0
    TI__Expert 7020 points

    Hi Reider, 

    The MSPM0's Open Drain pins require a 4.7kohm pullup instead of the R1 and R2 = 100kohm. It should be pulled up to CVDD's side. CVDD cannot touch the MCU's 5V or else CVDD will not turn on while it is connected to the MCU's 5V.

    Bypass capacitors and the IC power supply have the recommended values. The current GPIO configuration is fine. Cell sense, CB filtering, and Cell balance resistors are setup correctly. 

    Reider McFeely said:
    - Are external pulldown resistors for BQ79616 unused GPIO necessary, or can internal pulldowns be used?

    The external pulldown resistors are for reducing noise in a noisy environment. If there is not a lot of noise in the device's environment or load then the pulldowns would not be necessary. If there is noise a lot of noise that could come from the environment or load, then I would recommend to include the pulldowns.

    Reider McFeely said:
    - TVS diodes necessary for GPIOs used with externally mounted thermistors?

    TVS diodes are not necessary for the externally mounted thermistors.

    Regards,

    David

  • 0 in reply to David Ray
    Prodigy 45 points

    Thanks David, very helpful. 

    For the UART pullup values I was referring to this table in the BQ79616-Q1 datasheet:

    But makes sense given the open drain on the MSPM0's 5V tolerant pins that a lower pullup resistance is needed for proper driving. So should we instead have:

    - 4.7kohm on MSPM0 TX, 100kohm and 51pF cap on BQ79616 RX?

    - 100kohm on MSPM0 RX

    Clarifying question: The datasheet mentions that CVDD can supply 10mA for external loads in SLEEP and ACTIVE. CVDD and +5V are on the same net in our schematic:

    The only way the MSPM0 is powered during normal operation is via CVDD (excluding when programming the MSPM0). Is this the correct way to do this?

    Best,

    Reider

  • 0 in reply to Reider McFeely
    TI__Expert 7020 points

    Hi Reider,

    Reider McFeely said:
    The only way the MSPM0 is powered during normal operation is via CVDD (excluding when programming the MSPM0). Is this the correct way to do this?

    During shutdown, CVDD is at minimum 3.4V and can provide up to 5mA. During my testing with the MSPM0, my laptop 5V was conflicting with CVDD which would not be the case for your design. Since you are only using CVDD to power the MSP, then the configuration is fine as long as no more than 5mA are being drawn by the MSPM0.

    Reider McFeely said:

    So should we instead have:

    - 4.7kohm on MSPM0 TX, 100kohm and 51pF cap on BQ79616 RX?

    - 100kohm on MSPM0 RX

    Yes this would be fine.

    Regards,

    David