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BQ25895: sometimes does not charge when plugged in

Patrick Küry
Prodigy 20 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ24195, , BQ25890

Hi,

I have some strange behavior of the BQ25895. Sometimes it does not charge and turn the BatFET off, when 12V plugged in.
But no error is reported in the status register. The error mainly occurs when the battery level is lower. But only if Vbat is greater than Vsys_min.
At first I thought it was a problem from my layout, but the same behavior, I can observe with your eval board.

So I made some measurements and the behavior of Ibat is very strange.

In this picture you can see the the charging current from the battery. This is about 300ms after VBus is present.
You can see e big 20A discharge peek out from the battery for about 10us. But in the case of this picture, the battery will be charged correct after that event. And in the case it does not charge, the negative peek is about 7A bigger.
The behavior ist the same, either if i do not write to some registers.
If Vbat is smaller than Vsys_min, this peak disappears completely.

Here are the registers in both cases:

Register Dont Charge Charging
0x0 0x7a 0x7a
0x1 0x5 0x5
0x2 0x7c 0x7c
0x3 0x10 0x10
0x4 0x4f 0x4f
0x5 0xf3 0xf3
0x6 0x5e 0x5e
0x7 0x9d 0x9d
0x8 0x3 0x3
0x9 0x64 0x44
0xa 0x93 0x93
0xb 0x6 0x16
0xc 0x0 0x0
0xd 0x55 0x55
0xe 0x2f 0x3a
0xf 0x32 0x3d
0x10 0x51 0x5e
0x11 0xdf 0xdc
0x12 0x0 0x64
0x13 0x3a 0x3a
0x14 0x39 0x39

I have also a board with the BQ24195 which looks very similiar and there I can not observe some behavior.

Are you aware of this behavior and do you have a recommendation on what I can do about it.
Thanks a lot
Patrick

  • 0
    TI__Mastermind 19115 points

    Hi Patrick, 

    Thank you for reaching out via E2E and providing your measurements and the register readings from the device.

    Could you help to provide some more detail on your test procedure. 

    -What is the initial state of the device before attempting to plug in the 12V supply? The battery is connected, but is it powering any load attached to SYS output? Is it in OTG mode or is the BATFET turned off? Is this test being performed with a real battery or a battery simulator (i.e. sourcemeter)?

    The device's response to detecting a large battery discharge current (> 9A) is to turn off the BATFET and keep it disabled until a new input source plug in is detected or BATFET_DIS bit is cleared. Is there something in your system that you would expect to be drawing such large current from the battery? 

    Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 20 points

    Hi Garret,

    sorry for the late reply.
    The battery is connected and Vsys is available and no load is attached. It happens either OTG is enabled or disabled. I perform the test with e real battery.
    This behavior can be observed on my own board but also on the EVAL board (BQ25895EVM-664).

    In the meantime I have ordered the Eval-board with the BQ25890 and can observe the same behavior with a defference in the current. The discharge peak is is only 4A. But it depends on L1, if I replace the 1uH on the BQ25890 Eval-Board with the 2.2uH from the BQ25895 eval-board the current peak is also 20A.
    And I can see nothing on the eval-Board that could draw such large current.

    Regards,
    Patrick

  • 0 in reply to Patrick Küry
    TI__Mastermind 19115 points

    Hi Patrick, 

    Thank you for the additional information. Back to your initial question I am not aware of this sort of behavior on this device and I have not been able to replicate on the BQ25895EVM. 

    Below is the waveform I capture of battery current and VBUS when 12V input is plugged in.  

    -How are you currently measuring the battery current and what battery are you using?

    -Referring back to your original plot am I correct that it appears the battery begins to charge at 5A before the large momentary discharge occurs?

    -If possible can you provide me additional wave captures of VBUS, IBUS, VBAT, and IBAT when this occurs?  

    Best Regards,

    Garrett