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TPS65381-Q1: TPS65381

Steven He92
Expert 2125 points
Part Number: TPS65381-Q1
Other Parts Discussed in Thread: TPS65381A-Q1

Dear Sir,

I test TPS65381 EVM, I check VDD6(Vo=6V/ 0A) find PIN28(SDN6) switching waveform not regular(see below picture.)

Could you kindly provide some suggestion how to improve this waveform.

  • 0
    TI__Expert 8730 points

    Hi Steven,

    The control loop of TPS65381-Q1 is based on a hysteretic comparator with below principle. So, SDN6 signal may not look like any other switching regulators based on current mode or voltage mode topology. Can you please check and see whether your waveform is similar to the below explanation? Can you also check with with load, SDN6 switches with fixed frequency and duty cycle?

    This switch-mode power supply operates with fixed-frequency adaptive on-time control PWM.The internal N-channel MOSFET is turned on at the beginning
    of each cycle if the sensed voltage on the VDD6 pin is below the hysteretic comparator threshold. When
    the MOSFET is turned on, it is on for a minimum of 7% duty cycle (7% of fclk_VDD6). This MOSFET is
    turned off when the hysteretic comparator detects a voltage on the VDD6 pin above the threshold. The
    VDD6 regulator may skip pulses if the output voltage remains above the hysteretic comparator when the
    clock edge occurs. When the MOSFET is turned off, the external Schottky diode recirculates the energy
    stored in the inductor for the remainder of the switching period. The VDD6 regulator enters dropout mode
    (100% duty cycle) for a supply voltage below approximately 7 V on the VBATP pin.

    Regards,

    Murthy

  • 0 in reply to Krishnamurthy Hegde
    Expert 2125 points
    Dear Murthy,
    I will check your comment.
    Thanks for your explain.
    Steven
  • 0 in reply to Steven He92
    TI__Mastermind 20590 points
    Hi Steven,

    Since it has been over a week with no follow up and the switching waveform looks typical for the hysteretic architecture of VDD6 pre-regulator on the TPS65381A-Q1 I'm going to mark this thread as "TI thinks resolved". There are other threads on the E2E forum on this topic for further reference as well. Please respond if you question still isn't answered.

    Thanks, Scott