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BQ25622: The Vbus status and Vbus ADC raise up time

Kailun Liu
Expert 3123 points
Part Number: BQ25622
Other Parts Discussed in Thread: BQ25898, , BQ25898E

Tool/software:

Hi Team, 

In BQ25898, we used to utilize Vbus ADC result to judge charging status when adapter plug in. 

However, in BQ25622, test to find it takes longer time for Vbus ADC result raise up, which causes 0 be read by MCU. 

We need you help to check: 

The delay time from adapter plug in to Vbus could be read by MCU. 

Can we use MCU to read Vbus status to replace read Vbus ADC result, how long it takes for Vbus status register update?

Thanks and look forward to your reply!

  • +1
    TI__Mastermind 31970 points

    Hi Kailun, 

    Please see my comments below. 

    Kailun Liu said:
    Can we use MCU to read Vbus status to replace read Vbus ADC result, how long it takes for Vbus status register update?

    Yes customer can read VBUS_STAT in REG0x1E to determine if an adapter has been plugged in. I have verified VBUS_STAT register will update approx. 385msec after VBUS is connected. The register updates within a few msec of converter startup (i.e. VSYS ramp up). 

    I also checked the time for VBUS ADC measurement to be reported in REG0x2C. If battery happens to already be connected and powering MCU then ADC can report VBUS voltage within approx. 10msec by using 9 bit effective resolution and disabling all other ADC channels besides VBUS. Although if battery is not connected or dead the time from adapter plug in to ADC result is over 400msec. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    TI__Expert 3123 points

    Hi Garrett, 

    Thanks for your detail explain and test result. Apart from VBUS measure when adapter plug in, we notice that the drop of VBUS when adapter remove also take longer time than BQ25898E. Is that an expected behavior? 

  • +1 in reply to Kailun Liu
    TI__Mastermind 31970 points

    Hi Kailun, 

    There are various factors that impact how fast VBUS voltage falls after adapter removal and it is not something that was purposefully changed between BQ25898E and BQ25622 ICs. Factors such as amount of input capacitance, current draw through the IC at time of unplug, any pulldown/load on input side of converter, etc. will have an impact on VBUS voltage drop when adapter is removed. 

    If your customer needs VBUS voltage to reduce faster after unplug there is a register to force a 30mA discharge current at PMID (REG0x16[3]) or other option is add a weak pulldown on input side of IC. 

    Best Regards,

    Garrett