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Original question:

TPS563257: Variable output voltage with MCU control

TPS563257: load transient response

Zehui Li
Intellectual 540 points
Part Number: TPS563257


Tool/software:

Hi,

    We found peak voltage is too far away from the normal targat value during load transient. Using larger output capacitor can help it.

    My question is what measurement should we care during a load transient test? Is the peak voltage the only thing we care?

  • 0
    TI__Mastermind 18490 points

    Hi Zehui,

    We should care about the voltage overshoot and undershoot during a load transient test. I depends on whether the voltage change will cause problem on the load side device. Thanks. 

    Regards,

    Shipeng

  • 0
    TI__Mastermind 32101 points

    Hi Zehui,

    I would suggest you can check not only the peak to peak voltage. Pls also check like if you see any ringing. Ringing is the unwanted oscillation seen in a voltage or current signal when the input or load is changed very quickly. If the controller cannot correct the output properly, overshoot and/or undershoot can occur, until it is damped out according to the damping factor of the system. In the extreme case, the system becomes unstable and the output oscillates indefinitely at the frequency where the gain = 1 and phase margin is 0°. In a circuit with a positive phase margin, the oscillations decay and are limited in number.

    Simplifying Stability Checks (Rev. B)

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    Intellectual 540 points

    Hi Lucia,

        Thanks! I understand that. I can use bode plot to check stability. To make it clear, in time domain, we only check peak value? What about other mesurement like how long it takes to return to targat output?

  • 0 in reply to Zehui Li
    TI__Mastermind 32101 points

    Hi Zehui,

    Any ringing or oscillation is must required to check in order to make sure the stability (Of cource, bode plot is another way to show the performance of the loop stability). Others need to check include Vp-p and recovery time. These two specs related with what your load required.

    Thanks!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    Intellectual 540 points

    Hi Lucia，

         How to assess recovery time? Is it a problem if it's very long but Vpp is within required range?

  • +1 in reply to Zehui Li
    TI__Mastermind 32101 points

    Hi Zehui,

    If you find the recovery time is very long, usually it represents that the system may be unstable. Pls refer to below waveform for a almost unstable waveform:

    And you can also compare it to a critically damped system as shown below: 

    In this example, the regulator is stable. Since it is close to critical damping, the feedback-loop response is good.

    TPS563257 is DCAP3 control mode which will have very fast load transient performance with short recovery time.

    Thanks!

    BRs

    Lucia