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LM5122: maximum soft start time

Bo Zeng Peng
Prodigy 130 points
Part Number: LM5122

Hello,

In my application, we need to boost the incoming voltage from 11V to 80V with rated output current at 0.3 A. We need to provide high power (100W) for short time e.g. 50 ms to the load. 

Therefore, we would plan to use a 20 mF capacitor as output capacitance. 

Is there any limit on output capacitor for LM5122?

For soft start time, my rough calculaion is 8s. Does LM5122 support such long soft start time? In webench design tool, the maximum allowed soft time is set to be 10 ms. Is there any limit in practical situation?

Best regards,

Bo

  • 0
    TI__Mastermind 21720 points

    Hi Bo Zeng Peng,

    Thanks for reaching out with your question and for using considering the LM5122 in your design.

    There is not maximum output capacitor for the LM5122. The control loop compensation will just need to be adjusted accordingly to ensure the loop is stable.

    A very large capacitor will be need to meet the 8s requirement. If you can find a capacitor with a leakage current less than the current sourced for the SS pin then the 8s SS time can be supported. The other option is to disable hiccup mode. During start-up the device will run into the peak current limit and continue to charge the output capacitor. As the output capacitor is large and the nominal output current is low the output voltage should rise slowly without any overshoot.

    Please let me know if you have any questions.

    Thanks,

    Garrett