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TPS274160: There is a chance that PWMing the device will trigger FAULT pin

Weiwei Su
Prodigy 120 points
Part Number: TPS274160

when I use 250Hz PWM to drive the chip's EN pin there is a chance to trigger the FAULT pin, not sure which fault it was.

But the chance will be much higher if I change the duty cycle dynamically. i.e. change the brightness from dim to 100%.

It happens with or without load present. I thought this chip is PWM capable?

  • 0
    TI__Genius 15675 points

    Hello, 

    Our High side switches are PWM capable, but do note they are not meant for PWM applications higher than 2kHz. 

    Can you confirm you are using the version B of this device and DIAG_EN is high? 

    It is possible the device could be seeing an overload condition, reverse polarity event, thermal shutdown or thermal swing. 

    Could you please provide a schematic so I can confirm your current limit? Also please provide a waveform with VS, VEN, FAULT, and IOUT? 

    Best Regards, 

    Elizabeth

  • 0 in reply to Elizabeth Higgins
    Prodigy 120 points

    sorry for the delay,

    I'm using A version with DIAG_EN tied to 3V3 for always enable.

    And I was mistaken that when I mean FAULT pin is actually the ST pin that is getting triggered.

    when PWM it, the ST pin will be triggered after the falling edge of the PWM.

    OUTPUT is not being disrupted.

    (FAULT above is actually ST pin)

  • +1 in reply to Weiwei Su
    TI__Genius 15675 points

    Hi Weiwei, 

    Thank you for providing those waveforms! I would be additionally curious to see the VOUT waveform overlaid by the ST plot and zoomed in. 

    Since EN is low when ST is pulled low, the condition which is triggering ST low would have to be open load. 

    I suspect ST is pulled low due to some capacitance on the output holding the output high enough that the Vvs-Voutx <V(ol,off) condition holds true for the ~2ms you are seeing ST pulled low. 

    My recommendation would be to lower your output capacitance, add some pull down resistance on the output, or ignore the glitch through software. 

    Best Regards, 

    Elizabeth