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I would like to ask for some help in implementing short-circuit protection on outputs of a PCB. I have a PCB, which is powered with 12 V DC from an external PSU. This power line gets routed to PCB’s output connector in two ways: directly or through a relay controlled by one of the PCB’s processor. A simple diagram showing this is provided below.

enter image description here

The goal is to implement short circuit protection on all of the output connections in a way that when a short circuit occurs, the board does not reset itself but only the short circuited output is disconnected with automatic reconnection when the short-circuit is removed.

As it is now, a short-circuit causes the external PSU to activate its short circuit protection and powers down the whole board. After trying with resettable PTCs on each output, the situation improves slightly. The board goes down, the PTC disconnects and the board is powered back up even if the short circuit is not removed. My understanding is that the fuses are too slow compared to PSU's internal circuit protection.

The next option I am looking at are intelligent power switches (IPS), such as for example the L6375S or L6370. Not ideal though, since I would like of limit the current at max 1 A (those ICs have their output currents set at 0.5 and 2.5 A, with short circuit currents at 1.1 and 3.2 A). But it's a start.

Does anyone have any experience with IPS? Would they get the job done? Are there any other options you would recommend?

A big thanks to everyone for any ideas, comments or other input. Cheers!

p.s.: User can connect different loads to the outputs. While inductive loads are not expected, they can’t be completely ruled out. However, if ruling them out would lead to an elegant solution, I could probably live with that.

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  • \$\begingroup\$ If the output is disconnected, what is the mechanism for reconnecting it? Can you live instead with simple 1 amp current limiters i.e. is your input supply capable of supplying up to 4 amps whilst maintaining a 12 volt output? If not, then what if all four outputs are taking 0.99 amps each i.e. none are causing a trip but the total current draw is 3.96 amps? You need to think about all the scenarios. \$\endgroup\$
    – Andy aka
    Aug 20, 2021 at 10:01
  • \$\begingroup\$ Thanks for your comment. I've edited my question to include the desired reconnection method. It should be automatic (e.g, resettable fuse). Thanks for pointing that out. Power supply is able to source 4.5 A. So I guess just limiting the current on each output would be OK. As long as the rest of the circuit remains powered on and functioning. Could you perhaps point me towards an example of such a limiter? \$\endgroup\$
    – Casper
    Aug 20, 2021 at 10:36
  • \$\begingroup\$ A resettable fuse requires a power cycle so it's not automatic; it's manual. \$\endgroup\$
    – Andy aka
    Aug 20, 2021 at 10:50

2 Answers 2

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To complete and wrap-up this question, I am posting the solution I ended up using. I went ahead using a high side power switch with internal overcurrent protection. Below is an example with ITS4200S-ME-N. Alternatives exist though (ITS4200S-ME-O, ITS4200S-ME-P, BTS4142N, ITS4142N, ISP452 and probably others).

enter image description here

While the solution I ended up with was not suggested by anyone, I would still like to thank all who contributed to the topic.

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You should look into adding a Hot Swap™ controller such as LTC4210-1 with an appropriate external MOSFET. This IC has automatic retry after overcurrent event.

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    \$\begingroup\$ Thanks for the idea. Will definitely have a look. However, if I understand correctly, current limiters such as for example MAX17610 would get the same job done (+ some additional like OV and UV protection) with less external components? Am I right? And surprisingly, for a similar price tag. \$\endgroup\$
    – Casper
    Aug 23, 2021 at 6:33
  • \$\begingroup\$ @Casper MAX17610 would work too, it is definately a better choice for your requirements. It's got the FETs built in, so ensure that thermal pad is properly connected on that TDFN package. \$\endgroup\$
    – DSI
    Aug 24, 2021 at 14:12

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