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BQ24250: Charging current stuck between 400mA and 500 mA

Cédric raf
Prodigy 20 points
Part Number: BQ24250

Hello, I'm currently working on a charging project. The circuit is designed to have an input of 5V and charge a Li-Po battery (3.9V and 2200mAh). The goal of this circuit is to be able to have a charge current around 2A. So i've chosen Rilim and Riset according to the datasheet : 

Rilim = 135 ohms (max 2A)

Riset = 135 ohms ( Charge current = 1.85A as a first approach and will decrease when the circuit works to allow 2A)

The pins EN1 and EN2 can also be used to programe externally the charging. Since i want to use external settings, i've set EN1 to high ( connected to LDO with a pull-up resistor) and EN2 to low state (to ground).

The 5V input is managed by a TTI dc power supply set to 5.1V/2A (to counter line resistance so that Vin  ~5V). 

The circuit is wired as followed : 

4532.sch.pdf

The basic functionality of charging and DPPM work but the charging current cannot go above 500mA and hangs around 400-450mA, no matter the settings on Rlim/Riset are.

LDO is stuck at 2.9V during charging (?).

I've also tried changing the charging current using i2c with this library and using the test code : https://github.com/ambergarageDIY/BQ24250/blob/master/BQ24250.cpp

Thanks for any kind of help you have got, 

Best regards

  • 0
    TI__Guru**** 151535 points

    Hi,

    The LDO linear regulator output should be slightly below VIN and charger will not work correctly until it is.  Something is loading it.  Are you circuit the BOOT capacitor is installed correctly?  If you remove the other loading components on it, does the voltage go up?   The schematic looks reasonable.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    Thanks for replying, 

    The LDO's voltage only crashes when i plug the battery in and the 33nF cap is correctly plugged in. Referring the other posts, the voltage on the boot pin is supposed to be a squared wave around 10V since it's SW+LDO (voltage) right ?

    Using the qfn package, i've soldered the ic on an adapter to put on a breadboard. Is it possible that either there is a small soldering issue or the breadboard is causing this issue ? 

  • 0 in reply to Cédric raf
    TI__Guru**** 151535 points

    That is correct about the BOOT pin.

    A solder short is possible.  Can you power down the IC and use a DMM to measure the resistance from LDO pin to ground?

  • 0 in reply to Jeff F
    Prodigy 20 points

    I took a multimeter and measured 200k between LDO and ground.

  • 0 in reply to Cédric raf
    TI__Guru**** 151535 points

    Ok.  I would expect the LED and resistor to lower that some.  Is VIN at 5V?  Is PMID at 5V?    

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hello, Yes both PMID and VIN are at 5V. I tried changing breadboard and the current went a little bit higher 650mA. But I'm also getting different performances by swapping batteries. 

  • 0 in reply to Cédric raf
    TI__Guru**** 151535 points

    Cedric,

    REGN should not be affected by different battery.  I recommend you order a BQ24250EVM to test with.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hello, thank you for helping me.


    I had suspiscions at the beginning on what could limit the current. It would seem that the breadboard + circuitry played a big role in that. By Widening and shortening the high current paths, the most current i could achieve was about 0.8A. So I don't think the IC or the circuit in general was wrong, it was that the  IC couldn't pull as much current as it needed due to all the contact losses and parasitic capacitance and inductance present in a common breadboard. Hence why the LDO's voltage crashed as soon as I charged the battery. 

    Any current setting above the max that i stated ealier could not work, but anything lower was working. For example, using the resistors Rset and Rlim made for 2A charge would not charge at 2A but at the max of 0.8A. But programming for a charge at 500mA through either Rilim and Riset or I²C was working perfectly fine. 

    So i ordered a Boostpak just to check on an already validated circuit if my suspiscions were correct. 

  • 0 in reply to Cédric raf
    TI__Guru**** 151535 points

    Hi,

    I agree with your assessment.

    Regards,

    jeff