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BQ40Z50-R2: The alternative capacitor selection for PBI pin.

Jeff Chiu66
Prodigy 20 points
Part Number: BQ40Z50-R2

Hi there,

According to the BOM & schematic in user's guide, the capacitance of the capacitor connecting between PBI pin and signal-GND is 2.2uF and I'm following it for all the battery products design so far.

Recently, the 2.2uF part is getting harder to purchase from vendors or agents, no matter the size of 0805 or 0603, due to the material shortage. I'm considering to replace it by one 1uF or 2 parallel 1uF as the alternative plans.

Although the part specification states the PBI pin is a power supply backup input pin, there's no additional information to know how it works. So, I'm not sure what kind of verification that we have to do to verify if the alternative plans are workable and keeping its performance.

Could you help to comment,

1. if the alternative plans are workable? or any side effects?

2. Or, what kind of verification we need to perform to check them?

3. Any other I should pay attention to?

  • 0
    TI__Mastermind 25955 points
    Hi Jeff,

    What a great question. I'm looking into this with the hardware team to see if the capacitor is merely for decoupling or if ESR will come into play for stability.

    I will update this thread tomorrow with more information.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Jeff,

    2.2 uF is recommended for the design, however, 2 1 uF capacitors in parallel should work, and 1 uF capacitor may work, depending upon your application.

    To test, please populate the capacitor(s) and bring the device near brownout. Monitor the dataflash and ensure that there are no jumps in the dataflash, comparing the states of the flash before and after testing.

    If dataflash does jump, additional capacitance may be required.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Jeff,

    If the above response helped resolve your question, please click on the 'This Resolved my Issue' button below to improve the find-ability of this response for others that may have the same issue. Thanks!

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 20 points

    Hi Bryan,

    Thanks for the reply. based on your input, The following is my test plan. would you help to comment it?

    since the min supply voltage is 2.2V, 

    1. providing a normal supply voltage, ex, 12V for a 3-s pack, and read the data flash out, this is GG-1.
    2. providing a min supply voltage, 2.2V, modify some parameters, and dump the data flash after modification, this is GG-2.
    3. comparing GG-1 & GG-2, and check if the modification is correct.

  • 0 in reply to Jeff Chiu66
    TI__Genius 14985 points
    Hi Jeff,
    That sounds like a reasonable plan!