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| What does this symbol represent? |
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| redgear:
--- Quote from: james_s on September 26, 2019, 03:43:15 pm ---A bit more context would help. Where did the schematic come from? Is it a professionally designed product or some hobby circuit found online? It's possible someone used whatever random symbol they found or didn't really know what they were doing. --- End quote --- This schematic is a Reference Design from Ti for their BQ76930 fuel gauge. Guess, a professional should have designed it |
| redgear:
--- Quote from: T3sl4co1l on September 26, 2019, 10:56:58 am ---I don't see how a spark gap could ever activate when there's two diodes right nearby. Diodes that are themselves redundant -- did the designer not know that TVSs are regular diodes in the forward direction? Tim --- End quote --- D6 is a flyback diode, its purpose would be to clamp PACK+ near PACK-. It would be a pulse current when the discharge FET opens under load, have a fast response, and stand off the normal operation voltage of the battery plus any transient. |
| james_s:
--- Quote from: redgear on September 27, 2019, 06:02:22 am --- --- Quote from: james_s on September 26, 2019, 03:43:15 pm ---A bit more context would help. Where did the schematic come from? Is it a professionally designed product or some hobby circuit found online? It's possible someone used whatever random symbol they found or didn't really know what they were doing. --- End quote --- This schematic is a Reference Design from Ti for their BQ76930 fuel gauge. Guess, a professional should have designed it --- End quote --- That's why I asked, unless I missed something it was never mentioned what this was or who designed it, we are not psychic. My best guess is that it's a spark gap or gas discharge device intended to protect against ESD. |
| iMo:
http://www.ti.com/lit/ds/sluscd0b/sluscd0b.pdf 11.1.4 - esd pcb spark gaps Fig. 7 and 8 |
| T3sl4co1l:
Wow, that's dumb. Well, par for the course with app notes. FYI, spark gaps don't fire until huge voltages, among other terribly messy things. But a TVS (even a small one like a regular zener diode*) handles ESD just fine, so there's no point in putting a spark gap AND zener in there. The spark gap will never fire. Just stick with the one that's better anyway. *They're not usually rated for it, so it's hard to say how much they will actually handle (8, 15, 30kV?). The modern equivalents are small TVS singles or arrays, available in impressively small packages and with low capacitance**, specified for ESD and surge. Some are CSPs (chip scale packages) smaller than 1N47xx dies, so it can't be too bad. There may be optimizations in TVS dies, their actual construction, that improve survival at high power levels, that are lacking in zeners, I'm not sure. **If they're a few pF, they're probably a diode in series with a zener, which is messier (the zener has to be charged up to the signal's peak voltage, which won't help with, say, high speed data signals without error correction), but usually okay. Tim |
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