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current-limited load switch response time

david sun
Intellectual 330 points

Hello


I have a question about TPS22946YZPR

for hard short detection, the on time is 0.125ms. for a PWM driven switch, if the short only happens in  16us. then it off 16us. will it be able to detect the short. Fairchild FPF2174 can't detect this mode of short.


for 155mA limit. if the PWM drive out 320mA for 5ms, and 0 mA for another 5ms. (average is 160mA). will the chip report over current for 155mA limit.


Sincerely,

David Sun

  • 0
    TI__Expert 5275 points

    Hi David,

     

    The minimum blanking time is 7ms, so a short less than this time will not result in OC pin being pulled low to indicate a short being detected.

     

    On the question about 155mA for 5ms, while the chip will not report the OC condition it will limit the current.  Will the PWM signal be used to control the load switch?  If so, the switch will allows at least 375mA current for the first 8ms after being enabled. 

     

    Let me know if you have any other questions.

     

    Best Regards,

    Adam Hoover

    DLS Applications Team

  • 0 in reply to Adam Hoover
    Intellectual 330 points

    Hi Adam

    thank you for your prompt response, I have another question.  in datasheet page 9.


    I(off) Von = 0, Vin = 3.6V. Vout open, and Vout short to GND, are these represent two worst cast of the leakage current.

    how about Vout to 3.5V. what is the quiescent current in this case.


    Von = 0, Vin = 3.6V, Vout = 3.5V. is there any current flow back to the chip.

    thanks,

    David Sun

    thanks,

    David Sun

  • 0 in reply to david sun
    TI__Expert 5275 points

    David,

     

    The case where Vout = open is measuring just the quiescent current into the device.  The case where Vout is shorted to ground is measuring the leakge current coming out of the device.

    For the case where Von = 0V, Vin = 3.6V, and Vout = 3.5V, I would expect the input current drawn to be closer to the IIN(off) spec.  Also I do not think there will be reverse current flow back into the chip.  

    Will there be another power source continuously powering the output up to 3.5V?

     

    Regards,

    Adam

  • 0 in reply to Adam Hoover
    Intellectual 330 points

    Hi Adam

    we are going to use this switch to control a battery charging, we always have Vout from battery, we can confirm that Vin will always be there, so we don't worry about the reverse current back to Vin. because input will always higher then output. what I concern is that in off mode( we want stop charge after the battery is full), even the current not back to input, is there other path that cause the reverse current leakage from the Vout into the chip.


    in off mode, if we measure the Vout(open) will it same as Vin.

    thanks,

    David Sun

  • 0 in reply to david sun
    TI__Expert 5275 points

    Hi David,

      

    There is not another path from VOUT to GND inside the device, so as long as Vin will always be powered I do not expect there to be leakage issue into VOUT when the switch is disabled. 

     

    Regards,

    Adam