Andrew ZonenbergAug 10, 2024

Does anyone have data on actual current capacities / resistances of "0 ohm" SMT resistors?

I'm not seeing tolerances or maximum resistances specified, only a power rating, which makes it hard to figure out how much juice I'll lose if I use one as a jumper for a power net.

Show threadGraham Sutherland / PolynomialAug 10, 2024
@azonenberg if you look in the product catalogue for that series of parts you may find that they have a footnote that specifies the maximum resistance of 0R parts. (ordinarily the x% tolerance usually means "look for the 0R max resistance in the x% section of the product catalogue / datasheet")
Show threadGraham Sutherland / Polynomial

@azonenberg 0805 is about the smallest I'd go for 2A continuous.

as an example, here's Uni-Royal's speclist for jumpers:

Aug 10, 2024 at 8:12amWeb
Show threadGraham Sutherland / PolynomialAug 10, 2024
@azonenberg (whoops sorry this was supposed to be in response to your reply)
Show threadGraham Sutherland / PolynomialAug 10, 2024
@azonenberg for low voltage power path stuff it may well be worth spec'ing a shunt resistor since you then have a known exact resistance, and can calculate the drop and thermals.
Show threadAndrew ZonenbergAug 10, 2024

@gsuberland This is for the input protection of the 48 -> 12V IBC.

If things go according to plan I'll have a TPS16630 in parallel with an empty 0R footprint, this is my hedge in case something goes wrong with the 16630.

Worst case current would be around 1.6A, so 2A already includes some safety margin. Realistically, none of my near term projects are going to pull anywhere near that much power.

Show threadGraham Sutherland / PolynomialAug 10, 2024
@azonenberg 0805 is probably ideal then, assuming your manufacturer has similar specs. more than 20% margin for continuous operation, 300% margin for overload so it'll survive transient spikes but isn't so overkill that it won't fuse out during a major fault.
Show threadAndrew ZonenbergAug 10, 2024
@gsuberland Yeah I haven't picked a part yet, and if the TPS works well I won't need to. This is just me wanting to avoid another respin if TSHTF.
Show threadPeter BindelsAug 10, 2024
@azonenberg @gsuberland Why not use a fuse?
Show threadAndrew ZonenbergAug 10, 2024

@dascandy @gsuberland I have a 2.5A fuse upstream of it.

This is being used primarily as a soft start to limit inrush when hot plugging power, and also to provide undervoltage protection.

(It's also configured for current limiting and overvoltage protection because it has those capabilities and I figured it couldn't hurt to use them, but my primary OVP is a big zener TVS and my primary OCP is the fuse)

Show threadElectronic EelAug 10, 2024
@azonenberg @gsuberland this is a one-off board, right? you could always take a bit of thick solid strand mains wire and hand solder it onto the 0805 footprint. should allow way more than 2A
Show threadAndrew ZonenbergAug 10, 2024

@electronic_eel @gsuberland No, this is not a one-off.

This is the next generation of the 48V power supply I plan to use for all of my future large projects, and I want to get it right on this spin (I'm already several spins deeper than I had planned).

So I'm building in various backup/multi-stuff options so if the things I'm fixing on this spin don't work, I can get a working board one way or another with just BOM changes.

The 0R is one of those chicken bits, if everything goes well I won't use it. If my new input protection has issues I may be putting 1.6A through it at full load.