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BQ24161 status says "Charging" even though there is no battery present

Adrian Rothenbuhler53
Prodigy 160 points
Other Parts Discussed in Thread: BQ24161, BQ24161EVM-721, BQ24160

I am using the BQ24161EVM-721 evaluation board for the BQ24161. Using the GUI provided by TI, I can see that the charger is charging the battery from USB even though that I don't actually have a battery plugged in.... This is strange. I tried playing with the settings a little bit, but couldn't figure out what is wrong.

I took a look at the schematic of the evaluation board and noticed a huge 47uF cap sitting on the battery pin (in addition to a 1uF cap). The BQ24160/1 datasheet only shows a 1uF cap. So I removed the 47uF cap thinking that maybe this cap could trick the charger into thinking that a battery is there. Nope, it's still "charging from USB" (I am powering the board through USB).

This doesn't make any sense to me at all. All values are default. Any ideas why that's the case? I would expect the charger to report "battery not present".

  • 0
    TI__Guru**** 166826 points
    Was there a square-ish waveform at the BAT pin? Was termination enabled? What was input current limit setting (if HOST, I2C register but if standalone, PSEL voltage)?
  • 0 in reply to Jeff F
    Prodigy 160 points
    Doesn't look like a square-ish waveform to me. It jumps up to 3.6V (default Battery regulation setting), then it declines for about 17ms (looks like a cap discharging) and then it goes back up to 3.6V and stays there.

    When you mentioned the PSEL setting I started messing with the PSEL jumper with I2C not active and I can see that it is not charging when PSEL is low. It is charging when it's set to high.

    I've tried it in host mode too and always get the "battery normal" indicator (PSEL jumper set to HI).

    This looks like the battery detection depends on the current setting (PSEL). In other words, to ensure correct battery detection, does PSEL have to be set low initially?
  • 0 in reply to Adrian Rothenbuhler53
    TI__Guru**** 166826 points
    Battery detection uses the same circuitry as termination. Termination is disabled if input current limit is set to 100mA, which is the case for PSEL = 100mA.
  • 0 in reply to Jeff F
    Prodigy 160 points
    That's it, thank you!
  • 0 in reply to Adrian Rothenbuhler53
    Prodigy 160 points

    Jeff,

    Something is still a little fishy here....

    I understand that the battery detection is only active when termination is active, which is only when PSEL is not set to 100mA. However, when I set PSEL so that the EVM powers up such that the BQ24161 reports that the battery is not present and then go into high impedance mode, it switches back to "Battery Present and Normal". I could cope with that, but when disabling high impedance mode it stays there and still reporting that there is a battery. The same applies when toggling the _CD pin.

    Since the datasheet does mention that toggling the _CD pin should be done to clear certain errors, I would expect that the battery status would not be changed by this. What I'm finding is basically that if there is no battery present, I will only see that until the first _CD toggle. After that, the battery status indicator is not correct at all.

    Is there a workaround for this??? In my application I would like to detect when a battery is inserted/removed/not present.

  • 0 in reply to Adrian Rothenbuhler53
    TI__Expert 8690 points
    Adrian,

    The way to check for battery present in this case is if the current limit is changed to 150mA. If current limit is at 100mA while toggling _CD, HighZ Mode or TE (Termination Enable), the status will go back to "Battery Present and Normal" because termination is disabled when you have 100mA input current limit.

    Toggling HighZ mode: During HighZ, BATFET turns on (goes into supplement), which prevents termination unless termination is enabled (input current limit higher than 100mA, HighZ mode off and no supplement mode).

    Toggling _CD starts a new charging cycle, where termination can happen if termination is enabled.

    Toggling TE removes the termination status, thus giving you "Battery Present and Normal" if termination is disabled (having 100mA input limit).

    I suggest that whenever the host is checking for battery presence, change input current limit momentarily to 150mA and back to 100mA. This will trigger termination and will give you the correct status.

    Thanks,
    Steven