• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 435 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.

Original question:

BQ25798: BQ25798

BQ25798: Charging disabled

Carlos Valente
Prodigy 10 points
Part Number: BQ25798

Tool/software:

Hi Jeff,

We are currently experiencing some issues with our system, which consists of a 4S battery and an 18V/5W solar panel. Specifically, we have observed the following behaviors:

  1. VBUS and PMID Voltage: These always reflect the voltage of the PV panel.
  2. SYS Voltage:
    • When no battery is connected, the expected 12V for VSYSMIN is not present.
    • When the battery is connected, VSYS consistently matches the battery voltage.

Additionally, we have connected the STAT pin to an LED for visual feedback. The LED is always HIGH, indicating either the batteries are charged or charging is disabled. However, we can confirm that the batteries are not charged. The /CE pin is connected to ground, assuming the EN_CHG bit is set to '1' by default.

One potential deviation from the expected setup is the prog resistor, which is 17.35k instead of the specified 17.4k for the 1.5 MHz frequency.

Could you please advise on what aspects we should focus on while debugging this behavior?

Thank you for your assistance.

Best regards,
Carlos Valente

  • 0
    TI__Guru**** 166376 points

    Hi Carlos,

    PROG pin of 17.35k is okay.  When battery and solar panel is attached, what do the status and fault flag registers report?  Is REGN voltage close to 5V?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    Thank you for your prompt reply.

    We reviewed the datasheet for the IC and we read it could operate in standalone mode. Therefore, we haven't investigated the I2C registers yet.

    During our troubleshooting, we measured the REGN voltage and consistently observed 0V with a 40Ω resistor connected to ground. We thoroughly inspected the PCB for potential short circuits but found none. To isolate the issue further, we even replaced the IC with a new one, but unfortunately, the behavior persisted.

    We would appreciate your clarification on the following:

    • Is a 40Ω resistance between PGND and REGN an expected value within the IC's operation?
    • Given the consistent 0V reading despite replacing the IC, could there be an undetected short circuit on our PCB that we might have missed?

    Thank you for your time and assistance.

    Regards,

    Carlos Valente

  • 0 in reply to Carlos Valente
    TI__Guru**** 166376 points

    Hi Carlos,

    REGN must come up in order for the IC to function.  It is powered from PMID which is connected to VBUS through a FET (shown as a resistor on the datasheet).  Below is the REGN spec:

    5V/30mA = 166ohm.  5V/40ohm = 125mA which will collapse REGN.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    I removed the IC from the PCB and measured the resistance between REGN and GND, which was indeed 40 ohms. I also measured another IC from my stock, and it showed an even lower resistance of 13 ohms.

    During one of our tests, when we supplied 5V to VBUS, the LED connected to STAT blinked three times before turning off. Since this LED was also connected to REGN, it indicated that the IC was functioning briefly, it was not damaged.

    However, given that this low resistance is present in both ICs, it seems there's no way to prevent REGN from collapsing.

    Regards,
    Carlos

  • 0 in reply to Carlos Valente
    TI__Guru**** 166376 points

    Hi Carlos, 

    I do not measure that on my EVMs.  Not sure why you are measuring lower.  No other customer has had this issue.

    Regards,

    Jeff