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BQ25792: BQ25792 related issues

jeno.zhang
Expert 2855 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

HI,

Question 1: Use BQ25792 to charge a series of lithium batteries, and test the charging voltage of the battery to be around 2.6V. The waveform is straight for a long time, and there will be periodic peaks in the middle. Is this normal, or are there other issues?

Question 2: What is the difference in charging status between BQ25798 and BQ25792? Using BQ25798 to charge a series of lithium batteries, the test charging voltage is around 4.2V, with a sawtooth waveform.

Thanks！
  • 0
    TI__Guru**** 165886 points

    Hi Jeno,

    Regarding 1, there were older BQ25792 ICs that have an issue with getting stuck in trickle charge but we purged those ICs over a year and a half ago. Other than that, the only other issue with BQ25792 is when no battery is attached, charge is enabled and TS function is disabled.  In that configuration, the charger BAT and SYS pins reach OVP and the converter turns off briefly, which can result in SYS collapsing.

    Regarding 2, the BQ25798 does not have the above issues.  I recommend moving to the BQ25798.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Expert 2855 points

    hi Jeff，

    1. Customer analysis suggests that the issue may be caused by the counter. The problem is with large capacity lithium batteries, while small capacity lithium batteries are not a problem.

    2.Another question is about safe and fast charging. For example, if the battery fast charges 3A and the time is set to 5 hours, that is, the safe fast charging time is 5 hours. If it is fully charged within 5 hours, all indicator lights will be normal. If it is not fully charged after 5 hours or the threshold for constant voltage charging is not reached, will the charging stop? Is this understanding correct?

  • 0 in reply to jeno.zhang
    TI__Guru**** 165886 points

    Hi Jeno,

    If charge does not complete before the safety timer expires, charging stops and the indicator light blinks.  The safety timer can be set to 5, 8, 12 or 24 hours in REG0x0E.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2855 points

    Hi Jeff，

    What is the normal charging output waveform of BQ25792 and what should be the output voltage state? What is the output state and voltage without connecting to a lithium battery？

    Thanks！

  • 0 in reply to jeno.zhang
    TI__Guru**** 165886 points

    Hi Jeno,

    If charge is enabled from /CE pin or CE bit and there is no TS fault when battery is removed, the SYS and BAT output will pulse as the BAT and then SYS pins reach OVP, causing the converter to turn off for 30ms  If charge is disabled or there is a TS fault, then SYS is regulated to MINSYS voltage and BAT floats to ~2.5V.

    If the pulsing is an issue, then please change to BQ25798.

    Regards,

    Jeff