I have a protection circuit that is used to protect a motor driver and buck converter.

The buck converter in turn powers 328PB MCU, SIM800 modem and few other low power circuits (4 Volt)

As you will see there is no provision for inrush current or over voltage.

My primary concern is inrush current because both loads can handle voltage of 28V, not that my application should get any where near that.

As I am waiting for parts to arrive I connected battery direct to buck converter (no protection but simple flyback diode). This seems to have fried downstream mcu.

So Im thinking this is down to inrush current when I connected the battery?


This is the setup I plan to use when the parts arrive.

I would like to add that Im trying to keep the power down to a minimum (hence the buck converter), The LOADS require less
than 2mA at idle, and this will be the normal operation condition.

the peak power consumption will be 2.5A @4V(buck) and 3A @ 12V(motor driver).
I am not concerned with over voltage as stated the buck converter should handle that, but am looking to implement an inrush
current limiter with the smallest power loss in doing so.

TIA

 

I'm totally confused ........
We need a proper Schematic-Diagram,
and a complete description of what You are trying to accomplish, and why.

"Inrush-Current" is probably the wrong term.
Generally, Inrush-Current is caused by charging large Capacitors on start-up,
if anything, that should help to protect sensitive downstream Loads.

A SMPS will always be a little noisy, especially anything to do with "Flyback" type operation,
a Linear-LDO-Regulator after the SMPS will take care of that though.
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OK sorry about that.

consider the following


Do you think that the inductor could impose a high current upon battery connection? (connected via croc clips).

 

1)
What is the part-number for your Buck-Converter-Chip ? ( it's not a Flyback-Converter ).
( You could be a Pal and attach the PDF to your next Post )
2)
What Frequency is it set to operate at ?
3)
How did You arrive at the Values of the Output-Filter Components ?
4)
How did You arrive at the Values of the Compensation-Network ?
5)
What is the part-number for "D-2" ?, PDF-file ??
6)
What is the maximum-Load that the Regulator will ever see ?
7)
Does your Micro-Controller have an "On-Board" Linear-Voltage-Regulator ?
8)
Why are You using "4-Volts" ?, that seems like an unusual Voltage.
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In your first post, what is the purpose of Q4?
If it's to protect against that application of reverse voltage, D4 will likely blow when a reverse voltage is applied.

 

Generally, Inrush-Current is caused by charging large Capacitors on start-up,
if anything, that should help to protect sensitive downstream Loads.

I guess transformers can also be seen in the tiniest of ways as caps then. At least I am now employing an inrush limiter to avoid tripping breakers