Best practice for connecting capacitive load

I have a motor driver board which has a bunch of capacitors on it. When I connect it to the mppt2420hc, it always triggers a “E: Low-side undervoltage alert, ADC reading: 21808 limit: 36133”. Then a 300 seconds delay, then the load switch turns on and this error triggered again.

I looked into the code. I found in the main function, there is a function daq_set_lv_limits(). Which is periodically called to set the max/min value of low-side voltage depending on current voltage measure at low side. The default setting of min is 0.8 times of low side voltage. I set it to 0.4 times based on the readings in error message. And now it works.

So I am just wondering what is the best practice when I need to connect to a capacitive load(has large in rush when turn on and big voltage dip)? Is there any drawbacks of my modification? Could set a interval for this error alert say if the voltage is just dipped for a brief second, the error won’t trigger?

You discovered a very interesting and not trivial challenge with short circuit protections for load ports.

As you probably know, a capacitive load looks the same as a short circuit in the first few microseconds, which makes it hard to distinguish between an actual short circuit and a capacitive load. Some more explanations and a simulation can be found on

We are really talking about a couple of tens of microseconds here. If you wait for a few milliseconds to a second, your load MOSFET may already get damaged in case of an actual short circuit.

That being said, if you have a specific use case with a high capacitive load, it should be fine to lower the threshold.

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Thank you for the detailed explanations. The more I dig into your mppt design the more I found how much thought put into it. Really appreciate it that you make it open source and share with everyone. :wink: