LM51521-Q1: Time it takes for the output voltage to stabilize

Part Number:



What are the specifications of the LM5152-Q1?

When the circuit shown in the figure was created with Pspice,
the FET operates at 500kHz when voltage V9 is applied 6.5ms after power is supplied to V6.

When the V9 settings were then changed to apply voltage sooner than 6.5ms and operation was checked,

control over the FET became unstable and excessive ripple began to occur in the output voltage.

Are there any regulations regarding the time to apply a load on the output side for the LM5152-Q1?

Could you please let me know if there are any points I should check to determine the cause?


 V6:6.5V 、V9:12.5V FSW:488.5kHz

Best regards,


  • Partial correction
    Part Number: LM51521-Q1, but the correct answer is LM5152-Q1.

  • Hello takahashi-san,

    Thanks for reaching out to us via e2e.

    I have some questions:
    - Why do you start-up with zero load and then suddenly connect the load after a while?
    - Does the real application require that?
    - Is it not possible to keep the load permanently connected to the output of the converter?
    - Maybe you could enable the converter together with the (permanently connected) load instead?

    - Why are you using that controllable current source as a load?
    - We have not seen that before and we are not sure if this may cause any issues.
    - Can you please connect a resistive load instead?
    - If this resistive load needs to be switched on and off, please use for example a FET in series with the load for that purpose.

    Sudden load jumps from zero to full load are extremely challenging for any kind of converter.

    Also, the description, how to distinguish between the two cases is a bit vague.
    - Does "sooner than 6.5ms" mean after 6.4ms or much earlier?

    - As there is no resistive load in the beginning, can you tell if the FETs have stopped toggling after 6.5ms (because of an overvoltage status on the output)?

    Please let me know more details to understand the difference.

    Also, have you used the QuickStart calculator tool (excel sheet) to calculate the external components (inductor, sense resistor, capacitors) and the compensation network?

    Thanks and regards