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TPS25947: Question for changing ILIM resistor when ITIMER is worked

Kazuki Kuramochi
Genius 10765 points
Part Number: TPS25947


Hello Expert,

I plant to change ILIM resistor when ITIMER is worked. Then I have question for ITIMER's behavior.

I think ITIMER is charging ITIMER cap during internal OC comparator detected output current that is exceed ILIM which is defined by external ILIM resistor.
After then, device enable over current limit when ILIM cap exceed the ILIM comparator's threshold(1.07).
Also, ILIM threshold voltage is defined by current source linked with output current(182uA/A) and external ILIM resistor.

So I guess OC threshold is changed following external resistor value even if ITIMER is worked.
For example, ITIMER will reset immediately if ILIM value is changed to higher value against current output current by changing external resistor . Also, ITIMER will continue to charge ITIMER cap when ILIM resistor is changed as far as new threshold become higher than current output current.
In other words, ILIM threshold is changed immediately if ILIM resistor is changed regardless of operating condition.

Is this understanding correct?


Best regards,
Kazuki Kuramochi

  • 0
    TI__Guru* 79181 points

    Hi Kazuki Kuramochi,

    From the block diagram it can be seen that :

    1. When current is  greater than ILIM the OC signal is set. When OC signal is set ,it shorts the current source of 1.8uA to ITIMER pin which will cause ITIMER cap to discharge. 

    2. If ITIMER cap discharges below 1.07 because the output current is still above ILIM  then ITIMER_EXPIRED is set otherwise if output current falls below ILIM while ITIMER cap is discharging it will reset OC signal and disconnect current source from ITIMER pin and set ITIMER pin to 2.57v.

    So when ITIMER is discharging and you change RILM then:

    1. If output current is less than new ILIM it will reset OC and ITIMER capacitor will stop discharging and ITIMER cap will set to 2.57v.

    2. But if output current is greater than new ILIM it will set OC and ITIMER cap will continue to discharge.

    Hope that answers query.

    Regards

    Kunal Goel 

  • 0 in reply to Kunal Goel
    TI__Genius 10765 points

    Hi Kunal,

    Thank you for your support.

    I understood that my expected behavior is correct.


    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Guru* 79181 points

    Hi Kazuki Kuramochi,

    Thank you. I am closing the thread now.

    Regards

    Kunal Goel