I have designed a new circuit using two MPM3620s for 5V and 12V with a 24V input. However, when powering up, I am having frequent failures, output shorting, and input trace burning. This seems to happen when hot-connecting the 24V. Do you have any suggestions on how to protect the MPM3620?
Also, I changed the EN resistors to 200K.
Hi Ghermann,
The schematic looks ok. May I know the reason behind adding a fuse at the output of the module?
This IC has an internal over current protection. Check out the note below from the datasheet.
In addition to this, may I know what type of failures are you observing?
Are you not able to see the output voltage of 5V & 12V at all?
“hot-connecting the 24V” What do you mean here?
Regards,
Adhish
EN resistor 200k looks good for an max input voltage of 24V.
When you hot plug, the input can ring to 2X the nominal supply. Put a TVS on the supply, or don’t hot swap it, or put a parallel electrolytic cap with lots and lots of ESR. Fiddle around in a simulator with hot swapping, or put a scope on Vin at the chip when you hot swap
The output fuses are just to add a little bit of added protection, maybe they are not needed. I’m using a 24v supply with a barrel connector for bench testing. When I connect the 24v, I get a spark and the smoke comes out of the MPM3620. The output is shorted to ground and to the input. The input trace usually burns out. After my original post, I added a 1uf capacitor (C90) from EN to ground to delay the enable at power up. That seems to be working. Does that sound like a proper solution? I’m hoping for a solution.
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Thanks for the suggestions. Do you mean a capacitor with a low ESR? I have two 10uf ceramic capacitors on the 24v.
Hi Ghermann,
I am glad to hear that adding a cap at EN pin worked out for you as a soft start.
Since you are operating at 24 Vin with barrel jack, spikes are likely to be seen and there is a chance it is exceeding the absolute maximum rating of the IC which is 28V.
In such case, I would recommend to add some sort of protection at input such as an E-fuse OR supressor diodes. I agree to the fact what jshannon said, adding big capacitors at input with low ESR are recommended because it will respond to the sudden change in voltage with a lower impedance during the spike itself. Refer this note below from the datasheet.
Regards,
Adhish
I added some TVS diodes and extra capacitors. Hopefully that’ll help.
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