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I have an issue with the following schematic:

enter image description here

When I am doing a hot swapping on the RS422 (Local console) connector X1200, my fuse F1200 blow up. I have a TVS diode to protect against overvoltage on power line (+36VDC) against ESD. However I don't have TVS diodes on Tx, Rx, gnd lines. Can it be the issue ? How could I prevent my fuse F1200 to blow up if the user is doing a hot swapping ?

I already check the fuse sizing and the typical current used is about 1 A, so it can't be a fuse sizing issue.

Additional information: VSL is +36 VDC and its power coming from an external power supply. This power is sent directly to pin 6 of connector X1200 in order to power supply an external circuit which is a console (containing a display unit, touchscreen, ssd.... (small computer)). This power supply is received by the external circuit then buffered. In the following picture you will see reception of the power supply by the external circuit.

enter image description here

Thanks for your help, Regards,

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  • \$\begingroup\$ How are the grounds related in the different devices you are connecting/hot swapping? \$\endgroup\$
    – Math Keeps Me Busy
    Commented Mar 24, 2021 at 15:08
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    \$\begingroup\$ I am bothered by the ferrite bead you have between pin 5 of your DB-9 connector and ground. Please read the answers to this question. \$\endgroup\$
    – Math Keeps Me Busy
    Commented Mar 24, 2021 at 15:33
  • \$\begingroup\$ Ground between both devices are connected together with a SMD Common Mode Line Filter (Würth Elektronik, ordercode 744273222) \$\endgroup\$
    – Armand
    Commented Mar 24, 2021 at 15:46
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    \$\begingroup\$ wow, 1.5A slow blow! This has nothing to do with ESD. Most likely you have huge bypass capacitors somewhere. If it was male plug I'd also consider accidental shorting of the power pin to the ground or shield, but you seem to have female socket there. TVS protection on external comm lines is always a good thing, but again, it has nothing to do with that fuse. \$\endgroup\$
    – Maple
    Commented Mar 24, 2021 at 16:27
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    \$\begingroup\$ Other problems not related to your main problem: 1) the ferrite(?) on the signal ground does no good but might cause ground problems. 2) you need the same resistor solution on your Tx differential pair as on the Rx one. 3) I don't get what R1200 and R1202 are good for. Do you have another board-to-board on the left side of the schematic where you expose UART to connectors? If so, and R1202 is for ESD, then why isn't there a similar resistor on the other line? 4) Your TVS is too weak for industrial use. Rule of thumb: 600W for industrial, 1500W for automotive. \$\endgroup\$
    – Lundin
    Commented Mar 25, 2021 at 10:20

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