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BQ25792: BQ25792 IC not charging fully discharged battery.

Nakka Malesh
Prodigy 130 points
Part Number: BQ25792

Greetings,

                 We are using BQ25792 IC in our Project requirement for charging a SES Intelligent battery 14.4 v battery(4S mode). Charging of the battery working fine when the battery in good condition, But when the battery fully discharged, charger doesn't charging the battery. BQ24792EVM charging the dead battery also. we find that EVM generating pulses to wake up the battery from dead condition but BQ25792 IC not generating pulses even though we are used the same Hardware scheme of EVM in my project. If there are any suggestions please reply me.

for your reference i'm attaching battery datasheet.

Battery charger scheme is same as BQ25792EVM.

Best Regards,

Malesh Nakka

  • 0
    TI__Guru*** 143870 points

    Hi Malesh,

    Can you send a scope shot of V(BAT) when this is happening?  Does V(BAT) ~=2.5V?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 130 points

    Hi Jeff,

                 Yes you are right VBAT is at 2.5V when CE pin goes low.

            I'm attaching screen shot of scope of VBAT voltage. It was 2.5V when CE pin LOW for 5Sec, and 0 when CE pin is HIG for 5Sec.

  • 0 in reply to Nakka Malesh
    Prodigy 130 points

    Hi,

                    We are Intentionally toggling the CE pin for every 5Sec.

    Best Regards,

    Malesh Nakka

  • +1 in reply to Nakka Malesh
    TI__Guru*** 143870 points

    Hi Malesh,

    Unfortunately, you have received one or more ICs that were production tested incorrectly and cannot exit trickle charge.  Some units work correctly if you disable PFM mode (REG0x12b4).   If you connect a partially charged battery, the charger works correctly.  You can return the failing units for a refund or replacement. We only recently found the issue and updated the test program so inventory with ICs from the new test program still low.

    Please note that the BAT and BATP pins are only 20V rated.  If your application requires you to hotplug a charged 4S battery pack, I strongly recommend adding a TVS between BAT and GND, if not using a shipFET, or adding a small capacitor (0.033uF) close to BATP pin to protect those pins from ringing above 20V at hotplug.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 130 points

    Hi Jeff,

              Thanks for your Response.

                                1. Will Updated IC's generates any spikes on BAT pin when CE pin is LOW? If YES, What is it's Voltage Range.

                                2. How to know whether it was old IC or Updated IC?. Is there is any updation of version number in REG48 of charger?

    Best Regards,

    Malesh Nakka

  • 0 in reply to Nakka Malesh
    TI__Guru*** 143870 points

    Hi Malesh,

    I don't understand question1.

    Regarding 2, the ICs with updated test program started shipping in March 2022. Unfortunately, the register cannot be updated. You can use the top marking date code 

     TI YMS where Y>=2 and M>=3 have the new test program.

    You can self screen out bad units as their battery voltage will not rise above 2.5V with no battery attached.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 130 points

    Hi Jeff,

                    Thank you for your valuable response.

          Regarding 1st Question:In updated IC's when there is no battery/ fully discharged battery connected and CE pin is LOW, what will happen to voltage on BAT pin?

    I found in evaluation board that it generating voltage spikes of  0 - 17.2V for every 2 seconds to wake up the battery from dead condition(actually my battery will internally cutoff the voltage when fully discharged(below 12.4V). To wake up the cutoff battery we need to give some voltage spikes externally). Is the same thing happens with updated IC's

    Best Regards,

    Malesh Nakka

  • 0 in reply to Nakka Malesh
    TI__Guru*** 143870 points

    Hi Malesh,

    The BQ25792 ICs which do not get stuck in trickle charge (current or updated ICs) overshoot on BAT and SYS at power up when no battery attached.  Ideally, with a discharged battery attached, there is no overshoot because the protector FETs close.  When the overshoot occurs, the converter stops switching briefly. Adding more capacitance on BAT (>220uF) and lowering input current limit and/or charge current at startup prevents the overshoot.

    Regards,

    Jeff