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TPS61150A: PWM Signal

Part Number: TPS61150A

Hi TI,

My customer has a issue with TPS61150A.

Applying the pwm signal independently results in an IOUT voltage drop(0.5V).

Please refer to the below waveform.

If SEL1 and SEL2 are connected and one signal is applied, there is no voltage drop.

  • Hi Mason,

        I don't understand your question clearly. Could you share us the schematic that you tested with above question? 

    Regards

    Sean

  • Hi sean,

    I've attached the schematic.

  • Hi sir,

        What's your input voltage for this test?

        Please remove R284 and R113 since there are pull-down resistor in the device.

       What's your test process when you observed the voltage drop?

        What's your meaning of "If SEL1 and SEL2 are connected and one signal is applied, there is no voltage drop."

    Regards

    Sean

  • Hi Sean,

    Input voltage is 3.3V.

    SEL1 and SEL2 are connected as shown in the circuit diagram below.

    : When SEL1 and SEL2 are connected as shown in the circuit diagram below.

  • Hi Mason,

         How about the phase between the two PWM signals when you do the independent test?

         And have you measure the output current of each channel when you do the independent test and together test? Have you found any current change when you do the test?

         Since for our LED driver, what we want to do is to make the output current constant and there may some voltage transient since you are using PWM dimming, but if the output current keeps no change, that's ok.

    Regards

    Sean

  • Hi Sean,

    Phase is about 60degrees?

    Please refer to below waveform.

    Does it need 180degrees?

    º

  • Hi Sean,

    Phase is about 60degrees?

    Please refer to below waveform.

    Does it need 180degrees?

    º

  • Hi Mason,

        No, the phase is not important, have you checked the output current? Is that correct when you change the phase between those two PWM signals?

    Regards

    Sean

  • Hi Sean,

    I've checked reduced output current from 10mA to 2mA.

    PWM frequency: 20kHz

    Duty: 55%.

    You mentioned removing pull-down resistor(4.7k). And TPS61150A has an internal pull-down.

    Can this resistor cause this problem?

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    Can this cause this problem?
  • Hi mason,

        That depends on the output impedance of the PWM signal pins, it may affect the signal amplitudes, but I also suggest you to measure the output current with different PWM signal connection.

    Regards

    Sean

  • Hi Sean,

    Can you guess the reason why the output current is reduced by the PWM connection?

    Removing the resistance does not solve the problem.

  • Hi Mason,

        I'm sorry that I can't guess what's the reason, could you do more test and check more detailly, thanks.

    Regards

    Sean