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Original question:

BQ24295: Very Slow Charging in Standalone Mode

BQ24295: Not charging or charge extremely slow

Giovanni Troncoso
Prodigy 20 points
Part Number: BQ24295

I design a PCB that has a 9-36V input, this goes into a buck converter to 5V, then this converter feeds the BQ24295, but seems like the batfet doesn´t turn on. I have done many meassures, the 5V output of the buck is really stable (it meassures 5.07V), when i meassure the Vsys it goes about 3.8V with no battery, and 3.5V with battery plugged in, when i meassure the battery voltage when plugged in it has the same value when it isn´t plugged, like the batfet is NOT on. I also checked the registers but the only thing weird is that is says is DPM, which is very strange, because the input voltage is above the 4.7v minimum and the current is very low (with the power supply it says about 30mA of the whole board at 12V, so at most 100mA at the 5V input of the charger, so also very far from the input current limit set to 2A). I also realize that the fault register is triggered on the 7th bit, but this seems to be ok, since i´m just reading the registers and not actually writting into them, so it would be in a "standalone" mode, as the datasheet says.

I´m even considering to look for an alternative IC.

There is something i have wrong on the schematic?, is there any advice on how to solve this?

i leave the schematic and registers:

Reg: 0: INT: 94 | BIN:01011110
Reg: 1: INT: 59 | BIN:00111011
Reg: 2: INT: 32 | BIN:00100000
Reg: 3: INT: 17 | BIN:00010001
Reg: 4: INT: 178 | BIN:10110010
Reg: 5: INT: 156 | BIN:10011100
Reg: 6: INT: 147 | BIN:10010011
Reg: 7: INT: 75 | BIN:01001011
Reg: 8: INT: 173 | BIN:10101101
Reg: 9: INT: 128 | BIN:10000000

  • 0
    TI__Genius 12485 points

    Hi,

    It does appear that the device is in some kind of DPM which can limit the charge current. Is there a load on SYS that may be pulling current?

    Giovanni Troncoso said:
    battery voltage when plugged in it has the same value when it isn´t plugged, like the batfet is NOT on.

    The battery is likely to stay the same voltage even while charging since the BAT pin is dominated by the battery voltage. This voltage will increase as the battery charges.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 20 points

    Hello!, 

    Yes, there is load on SYS, but there is no chance it is drawing too much current (it could be at most 100mA, and i´m being very exaggerated), and as far as i undersatand the DPM is mostly based on the input rather than the output, and there is a very stable 5V input and no greater consumtion in the source (at most 100mA in the 5V input of the charger).

    Another thing is that i leave the battery plugged in over the night and found out it was charging, but really slow here are the conditions:
    The battery was at 3.31V when i plugged it in, Before plugin in the battery my bench power supply says it was drawing 10mA@12V, and when i plugged in the battery it says 30mA@12V. Today when i meassure the battery voltage it was about 3.5V (both meassuremente where taken with the battery disconnected from the PCB).

    I´m going to play arround with the d+/d- resistors to see if there is some weird behaviour affecting from there, i don´t see how that could impact, but i have run out of ideas. Any idea for testing or anything i would really appreciate.
    Thanks again Juan!, you helped me out with the first design of this circuit, when i had no output on the Vsys, it seems that the problem was that since it didn´t had any connections on the d+/d- pins it tought it didn´t had anything plugged in so it didn´t start the buck, but i´m going to test that now too, removing the D+/D- ressitors and see its behaviour.

  • 0 in reply to Giovanni Troncoso
    TI__Genius 12485 points

    Hi,

    Giovanni Troncoso said:
    Yes, there is load on SYS, but there is no chance it is drawing too much current (it could be at most 100mA, and i´m being very exaggerated), and as far as i undersatand the DPM is mostly based on the input rather than the output, and there is a very stable 5V input and no greater consumtion in the source (at most 100mA in the 5V input of the charger).

    In that case I would check the input current limitations since, as you mention, the SYS load is not very high. And please keep in mind that VDPPM is caused when the load on SYS exceeds the amount of current that can be pulled from the input (whether limited by the IC's input current limit or by the VINDPM feature).

    Giovanni Troncoso said:
    Any idea for testing or anything i would really appreciate.

    I would try and isolate the current path by removing the SYS load and then checking what the DPM status is. If it is still in DPM then that would be a clear indication that the input current limit is what is limiting current to the battery. In which case the D+/D-, INLIM, and VINDPM settings would be the next step in debugging.

    Best Regards,

    Juan Ospina

  • 0
    Prodigy 20 points

    I solved it, it was the most stupid thing ever, cheking on the manufacturer BOM, i realize the ILIM resistor that placed wasn´t of the value i needed, it was about 14k, so it limits the input current dispite the register value. That´s why it shouwed up in "IIN_DPM"

  • 0 in reply to Giovanni Troncoso
    TI__Genius 12485 points

    Hi Giovanni,

    I'm glad you were able to resolve the issue.

    Best Regards,

    Juan Ospina