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BQ25170: Not able to charge the discharged battery

Hitesh Gambhava
Prodigy 140 points
Part Number: BQ25170
Other Parts Discussed in Thread: BQ24040, BQ25185

Tool/software:

Hi TI team,

I have used BQ25170 battery charger for 1S Lipo battery. Designed works fine when battery voltage >3V. It is working normaly during charging phase.

When battery is in discharge mode i.e. 0V (Cut off from PCM). BQ25170 is not able to charge it. It shows 1.4V at VOUT pin of the IC.

Strange behaviour - If I do multiple times plugged in-out USB cable at 3rd of 4th attempt everytime it starts charging.

Attached the schematic diagram for your reference.

Looking forward to root cause and solution for this situation.

Best Regards,

Hitesh

  • 0
    TI__Guru* 75606 points

    Hi Hitesh

    This problem could be caused by the OUT short circuit feature, Battery Short.  When OUT voltage is below 2.2V the current is limited to 16mA.  The low current will reset the PCM or increase battery voltage to higher voltage to start safe charging.

    If the System Load is connected to the battery, it will prevent battery voltage from increasing above 2.2V and increasing output current.  

    Check system load and decrease if possible.

    Update - Vbat short voltage is 2.2V for li-ion and 1.2V for LiFePO4.

  • 0 in reply to Bill Johns
    Prodigy 140 points

    Hi Bill,

    I tried with fully disconnecting system load only battery connected at the charger output. I am still facing the same issue. Is there something charger is not able to see the deep discharge battery while PCM path is cut off?

    Best Regards,

    Hitesh

  • 0 in reply to Hitesh Gambhava
    TI__Guru* 75606 points

    Hi Hitesh

    Can you check the current going into the BQ25170 it should be 16mA when battery voltage is less than 2.2V?

    What voltage are you seeing on the BQ25170 output and is it increasing?

  • 0 in reply to Bill Johns
    Prodigy 140 points

    Hi Bill,

    We are seeing 1.547V at output. It is not increasing even after 2-3hrs of charging.

    Best Regards,

    Hitesh

  • 0 in reply to Hitesh Gambhava
    Prodigy 140 points

    Hi Bill,

    BQ25170 is taking current 16.87mA.

  • 0 in reply to Hitesh Gambhava
    TI__Guru* 75606 points

    Hi Hitesh

    This is looking normal for the BQ25170 in a battery short mode with output voltage below 2.2V.  Current will be limited to 16mA.

    Is the current going into battery or part of the system?

    If you disconnect the battery and system load do you get the VOUT (BAT) waveform from datasheet figure 8-3, Power Up Without Battery?

  • 0 in reply to Bill Johns
    Prodigy 140 points

    Hi Bill,

    Sorry for the late reply. Yes, we are getting the same waveform as per figure 8-3 without battery (with and without system load scenario).

    What could be the issue here, any further insight?

    Best Regards,

    Hitesh

  • 0 in reply to Hitesh Gambhava
    TI__Guru* 75606 points

    Hi Hitesh

    Hitesh Gambhava said:
    Yes, we are getting the same waveform as per figure 8-3 without battery (with and without system load scenario).

    Bill J - This is a good sign.

    What can you tell me about the battery? 

    Something to try:

    Does increasing charge current help, R7 (1k) to a higher value help?  

    BAT_SHORT current is limited to 16mA and will be 16mA independent of R7.

    After the voltage rises to 2.2V (precharge) current is 20% or R7.  For 1k that is 60mA. Possibly higher prechage current will help.

    Something to consider:

    Another TI device, the BQ24040 has a Battery Short voltage of only 0.8V with similar current, 15mA.

  • 0 in reply to Bill Johns
    Prodigy 140 points

    HI Bill,

    I increased the Charge current with Iset=600ohm but the situation is same. Is it means this battery charger can not work where we directly connect load to VBAT?

    Best Regards,

    Hitesh

  • 0 in reply to Hitesh Gambhava
    TI__Guru* 75606 points

    Hi Hitesh

    What can you tell me about the battery?  Do you have a data sheet?

  • 0 in reply to Bill Johns
    Prodigy 140 points

    Hi Bill,

    I tried to find battery datasheet but its local made so couldn't get. Its Lipo battery pack with PCM on it. I tried with 2-different battery but the same scenario.

    Can you help me understand - what could be battery charger will provide current on Vout pin when it sees no battery at that pin? because once PCM cutoff then it will not see battery until precharge states starts? Do you think it would to have trickle charging option inside the battery charger where we are sharing load + battery charging at battery charger output?

    --

    Best Regards,

    Hitesh

  • 0 in reply to Hitesh Gambhava
    TI__Guru* 75606 points

    Hi Hitesh

    Hitesh Gambhava said:
    what could be battery charger will provide current on Vout pin when it sees no battery at that pin? because once PCM cutoff then it will not see battery until precharge states starts?

    With the PCM cut off and no voltage at VOUT BQ25170 is in battery short condition.  Current will be limited to 16mA when voltage is 0V to 2.2V.  The deglitch time is 1mS rising or falling.

    NOTE that the LiFePO4 (LPF) setting - Current will be limited to 16mA when voltage is 0V to 1.2V.  As a test could try configuring as LPF.

    Hitesh Gambhava said:
    Do you think it would to have trickle charging option inside the battery charger where we are sharing load + battery charging at battery charger output?

    Tell me a little more about this idea?  

    We have some devices that separate out the battery and system load, Power Path devices. See BQ25185