• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 358 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Battery charging issue

??? ??
Prodigy 30 points
Other Parts Discussed in Thread: BQ25750

Hi,

Regarding the BQ25750 EVM device:  

We are experiencing an issue — the device is not charging the battery.

Device data:  

- Battery voltage: 22.5 V  

- Power source input voltage: 15.8 V  

- Input-to-battery switching threshold: 8 V (VAC is within the valid window)  

- Battery charging is enabled in the registers  

- The device is not in HIZ mode  

- Voltage on the RENG pin is 4.9 V  

- The registers indicate the device is in "fast charging" mode  

- Charging current is limited to 2.5 A, both via hardware and in the registers

However, charging is still not taking place.  

It’s important to note that the chip was damaged and we replaced it.

We would appreciate your assistance on this matter.

Thank you and all the best.

  • 0
    TI__Expert 8630 points

    Hi,

    Thanks for working with this EVM! I would like to see a few waveforms to see what is happening with the EVM. When the registers indicate "fast charging" mode, please provide the following:

    • The oscilloscope waveforms for TP18/TP19 - SW1/SW2
    • The voltage on TP4 - ACDRV
    • The voltage on TP2 - SYS
    • The voltage on TP15 - DRV_SUP

    Best,
    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 30 points

    7167.Tests.pdf

    Hi,

    Attaching the requested tests.

    Thanks.

  • 0 in reply to ??? ??
    TI__Expert 8630 points

    Hi,

    Thanks for sending over the waveforms! From the images, I notice that ACDRV, SYS, and DRV_SUP are within the expectation. SW1 and SW2 however, are not. SW1 should be constant at a value of around 15.8 V from the input voltage. SW2 should be switching from 0 to 22.5 V. Can you provide the following waveforms for me:

    • TP25 - HIDRV1
    • TP26 - BTST1
    • TP27 - HIDRV2
    • TP28 - BTST2
    • TP43 - LODRV1
    • TP44 - LODRV2

    These waveforms will let me know if the device is sending the proper signals to the switching FETs. It may also be helpful to check the soldering around the BQ25750 pins for SW1, SW2, and the pins mentioned above.

    Best,
    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 30 points

    Attaching the additional tests.3806.Tests.pdf

    Thanks.

  • 0 in reply to ??? ??
    TI__Expert 8630 points

    Thanks for sending over the additional tests. I see that the BTST1 node is at a constant 0 V. This implies that it is not charging up the BTST capacitor. Can you check the physical path from the DRV_SUP node to the BTST1 node and make sure no components are damaged/missing and that the soldering joints are good? This should be Diode D3, Resistor R13, Capacitor C12, and pin 26 BTST1 on the BQ25750.

    Best,
    Michael

  • 0 in reply to Michael Bradbourne
    TI__Expert 8630 points

    Hi,

    Just following up on this issue. Have you been able to get the device charging?

    Best,
    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 30 points

    Hi Michael,

    Thanks for getting back to me — it took me a bit of time.

    As you said, it turned out that resistor R13 was damaged. I removed the resistor and replaced it with a short.

    Now I’m encountering a new issue:

    When I power the device in a mode that allows charging (the PG LED is on), and the power is supplied only through the power supply (with no battery connected), the following happens:

    The STAT1 and STAT2 LEDs blink alternately — one turns on while the other turns off, switching about every quarter of a second.

    What seems to happen is that when the device tries to enter charging mode, the power supply hits its current limit (set to 5A), then charging stops, and the cycle repeats.

    Do you think this behavior is related to the previous issue?

    Also, how is it possible that the device enters charging mode even though no battery is connected?

    I’d appreciate your help.

    All the best.

  • 0 in reply to ??? ??
    TI__Expert 8630 points

    Hi,

    This seems like normal behavior. The device is charging the output capacitors. The device will be in constant current mode until the capacitors reach the charge voltage. The device will then enter termination. The capacitors will discharge and reach the recharge threshold starting the process over again. This is also why the STAT1 and STAT2 pins blink alternately (to indicate charging and charge finished).

    Best,
    Michael

  • +1 in reply to Michael Bradbourne
    Prodigy 30 points

    Got it. Excellent!

    Thank you very much!