• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 1867 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.

bq24314 operation when ILIM pin is shorted with OUT pin or VBAT pin

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: BQ24314

Our customer is concerned about device operation at pin to pin short condition. They would like to know the dvice operation when ILIM pin is shorted with OUT pin or VBAT pin. How does the device operate?

If current limit threshold changes, I would like to know changed value.

I will attach bq24314 schematic, and input voltage is 5V.

  • 0
    TI__Guru**** 166466 points

    When ILIM is shorted to OUT, there is a feedback loop that causes the current regulation level to reduce.  In my test, the current was reduced by a factor of 2.5.  The IC does not enter OCP.

    When ILIM is shorted to VBAT, the IC enters OCP because the voltage at ILIM exceeds ILIM reference voltage.  After 15 repeated current measurements during the blanking and current periods, the IC turns off the FET and current flow stops. 

  • 0 in reply to Jeff F
    Guru 10200 points

    Jeff-san,

    Thank you for your support.

    I have additional questions for your answer, thus pkease let me know.

    When ILIM is shorted to VBAT, I think ILIM threshold changes because VBAT is pull down to GND in our customer cirsuit. I think ILIM pin has pararel resistor of 20k and 100k. Is my idea correct?

    When ILIM is shorted to OUT, you said IC does not enter OCP. I couldn't understood this, I think 5V appears on OUT pin, does the IC enter OCP at that time because ILIM is 5V? Does the Out pin voltage drop by current limit operation? Thus,  doesn't IC enter OCP?

    What voltage is the ILIM reference voltage?

     

    Best Regards,

    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Guru**** 166466 points

    I did not notice your customer's VBAT pin was pulled to ground through a resistor.  So you are correct that tying VBAT to ILIM results in 20kohm||100kohm resistor, which changes the ILIM level.

    Regarding shorting to OUT, when I tested this on the bench, the current flowing through the pass FET reduced but continued.  And the voltage on ILIM rose from the 1.2xV reference voltage.  The only way for this to happen is if there is a new feedback loop.  From the block diagram, when I connect OUT to ILIM, I am essentially connecting the output of the ILIM error amplifier through the source follower back to the amplifier's negative input.