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LM61460-Q1: Sergy voltage related inquiry

MJ Jeon
Genius 5240 points
Part Number: LM61460-Q1
Other Parts Discussed in Thread: LM61460EVM

Hi, TI Support Team

The following inquiries have been received from customers.

Please answer, and if you have any data, please send it.

[condition]

Vin: 9~16V

Vout: 5V

Iout: 6A

In the above state, how much will the Sergy voltage occur in the start-up state or in the worst condition?

In addition, I am trying to apply a capacitor with a breakdown voltage of 16V to the output terminal, but is it okay?

Please ask for data or answers in a condition similar to the applicable conditions.

Thanks.

Regards,

MJ

  • 0
    TI__Guru 50120 points

    Hi MJ,

    I am not familiar with Sergy voltage, can you explain what this is?

    If you are wondering about the output voltage reading during a soft-start, please refer to Figure 9-8  and Section 9.3.10 for more information on this. 

    The soft-start would allow the output voltage to slowly ramp up to final voltage without much oscillation or overshoot. 

    Also it is generally recommended to have MLCC capacitors rated for double the expected DC voltage. In this case, it is recommended to use a 16V rated ceramic capacitor. 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Genius 5240 points

    Hi, Jimmy

    Sergy Voltage can be judged to be similar to the overshoot voltage you think.

    For example, at the point when the IC starts to operate, there are occasional symptoms of a voltage rise from Vout for a very short period of

    time, usually at Vout.

    You are inquiring about this voltage.

    I use the LM61460-Q1 in Auto mode, and I was inquiring about the voltage that rises when the operation starts in this mode.

    Even under the above conditions, would it be okay to apply a 16V withstand voltage capacitor as you said?

    Thanks.

    Regards,

    MJ

  • 0 in reply to MJ Jeon
    TI__Guru 50120 points

    Hi MJ,

    As mentioned the internal soft-start should prevent this type of overshoot and surge from happening. The soft-start reduces the sudden inrush current during startup and allows the output voltage to slowly climb up to final voltage. You can expect startup behavior similar to the power module Figure 51. Notice how there isn't any output voltage overshoot but instead output voltage slowly ramps up.

    If by 16V withstand voltage as in the capacitor rating then yes this should be okay for a 5V output application. Can you provide the actually datasheet for the capacitor just for my own review.  The LM61460EVM is currently using the following 16V rated output capacitors. I'd suggest you use them in your design as well. 

    Regards,

    Jimmy