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I'm designing a PCB in which the main ICs are a STM32F0 microcontroller and an INA226. These IC have some IO pins exposed in a header and the device will be handled by people.

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  • \$\begingroup\$ The devil is in the detail and that detail is the schematic around the header. \$\endgroup\$
    – Andy aka
    Mar 20, 2020 at 18:02

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It depends on what the headers head to. ESD is one thing but other types of damaging events can apply. Long wires, more than short wires, must be protected. Short wires or direct board to board, probably not, but a TVS against ESD adds to quality.

One problem can happen when users plug or unplug when it's hot (powered). Even worse when they plug connectors upside down. Even thought users are supposed to read instructions. Think about every scenarios before designing the protection. Sometimes a simple zener is enough. TVS diodes are used for medium to high frequency lines. They are better and more expensive. The best is to read the data sheet in search for a "typical circuit" schematic and other recommendations. Also try to find tutorials or application notes about them. for example this or this one

I would first put a resistor, the TVS diode, then a second resistor.

[pin header] --- vvv --- [TVS] --- vvv --- [ic]

The value of the resistors depends on the frequency. The higher the frequency the lower the value. Maybe no resistor at all for high speed. I can't answer for that. For very low frequencies or no frequency at all, I'd put 1k each. Depends on the type of signal.

The TVS should be connect to GND and/or Earth ground depending which type of surge or ESD you protect from.

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I'll partially agree with Fredled, but not the zener, you'll just blow out the zener and the IC with a good walk across the carpet.

Unidirectional TVS is the way to go for nearly everything. Don't use bidirectional ones unless you have a dual supply & you know what you are doing. Kelvin connect everything, ideally you have a trace from the connector to the TVS (co-locate those if possible, shorter=better), then a separate trace from the TVS to the IC (longer trace=better). If at all possible have the incoming trace on one side of the pad and the output on the opposite side of the pad. TVS selection should really be based on the level & frequency of ESD hits you are expecting. Cats walking thru a plastic tube on their way to an electronic scale & RFID reader is totally different than something that may get hit by a worker during assembly and maintenance. (I won't name the cat food brand, but I did consult for that situation and they didn't like my advice of simply shaving the cats...)

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  • \$\begingroup\$ About the zener it depends how critical the device is, grade requirement versus cost target and the type of signal, location, to and from what it's supposed to be connected etc. See cost difference between a quality TVS an a cheap generic 5V zener. When you have 16 I/O to protect you think about it. Protected with a resistor (as high as signal allows) the zener won;t be so fragile. On external data line of a certain speed, the TVS is of course the obvious choice. \$\endgroup\$
    – Fredled
    Mar 30, 2020 at 23:26
  • \$\begingroup\$ I'd feel a lot safer with schotky diodes clamping to the power supply if cost is that big of a concern. Most of your 4x and 8x TVS packages are a pile of steering diodes and a single avalanche device. \$\endgroup\$
    – grambo
    Mar 30, 2020 at 23:37
  • \$\begingroup\$ Yes, a shottky but in parallel with a TVS, a zener or a varistor. Whatever is the best for the application. I must check these 8x TVS. ;) \$\endgroup\$
    – Fredled
    Mar 31, 2020 at 0:11

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