• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 179 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

BQ25101: charging begins only when battery is connected to VOUT after 5V is connected to VIN.

Robb Zimmerman
Prodigy 10 points
Part Number: BQ25101

have RSET = 540Ω, and I have TS = 255kΩ to GND. Input capacitance is 10uF, and output capacitance is 1uF. I have a 370mAh battery (Jauch LP402535JU, 4.2V max charge voltage, 0.5C max charge current) connected to the output of bq25101.

I have observed some odd behavior when I connect 5V to VIN (i.e. plug in USB):

  • /CHG does not go low to illuminate the charging LED; and
  • output voltage does not increase until ISET is reached (i.e. VOUT = VBAT); and
  • no current draw on the power supply.

However, it gets interesting. If I disconnect the battery, then connect 5V to VIN, and then re-connect the battery:

  • /CHG goes low, illuminating the charging LED; and
  • output voltage is slightly above open circuit battery voltage, i.e. it's clearly in constant current charging; and
  • 5V VIN current goes to slightly above ISET current. (I’m confident that if I measured the current at VBAT it would be equal to ISET.)
  • Subsequently, if I disconnect battery and then re-connect battery, 5V VIN current resumes at slightly above ISET, but /CHG does not remain low (i.e. the battery is charging, but /CHG doesn’t illuminate).

It seems clear that I can create conditions in which this part functions as expected. However, I haven’t found the logical explanation for why it functions only when USB is plugged in BEFORE battery is connected. It could be a part issue, or it could be a solder process issue, or it could be a PCB issue. I have confirmed the parts on the PCBA match the design values.

Can anyone help diagnose what is happening here?

  • 0
    TI__Mastermind 19195 points

    Hello Robb,

    Can you share the schematic and waveform showing the issue?

    The charge pin is pulled to GND during the first charge cycle only (independent of TTDM) and is turned off once the battery reaches voltage regulation and the charge current tapers to the termination threshold set by the PRE-TERM resistor.

    A new charge cycle is started when a good power source is applied, performing a chip disable/enable (TS pin), exiting Termination and Timer Disable Mode (TTDM), detecting a battery insertion or the OUT voltage dropping below the VRCH threshold.

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    Prodigy 10 points

    UPDATE: I tried changing TS from 255kΩ to float, and all units worked as expected. I believe in TTDM disable mode there is a state where a connected battery is not detected, thus disabling charge, but I don't understand why it's not detected.