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Use a dedicated USB protection IC instead of a regular fast-blow fuse #34

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whitequark opened this issue May 3, 2018 · 6 comments
Closed

Use a dedicated USB protection IC instead of a regular fast-blow fuse #34

whitequark opened this issue May 3, 2018 · 6 comments
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hardware Component: hardware revB Hardware revision: B
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@whitequark
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If you short Vio to GND for like a millisecond it blows instantly. Source: shorted Vio to GND for like a millisecond.
@whitequark whitequark added the revB Hardware revision: B label May 3, 2018
@awygle
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awygle commented May 5, 2018

I'm not sold on this change yet, I'd like to discuss.

Here's an example PPTC fuse (probably our best option): https://www.mouser.com/datasheet/2/643/0ZCJ_Nov2016-1132002.pdf

It's got a 500 mA range between hold (guaranteed not to trip) and trip (guaranteed to trip), takes 100 ms to trip (at 8A!), and has a max resistance of 700 mOhms. That's a drop of 350 mV at full draw, and 100 ms seems very slow to me.

The tradeoff, to me, is between "it's a dev board, our audience is likely to pop fuses" and "fuses, when popping, should pop very fast".

Thoughts?

@awygle
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awygle commented May 5, 2018

Mouser product page: https://www.mouser.com/ProductDetail/Bel-Fuse/0ZCJ0050FF2G?qs=sGAEpiMZZMsgjL4JkW1EEcd%252bb5fzYQwTc0AQKqNICHhbBLu5swCw1w%3d%3d

@whitequark
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This fuse will take ~1s to trip at 1A fault current. Seems completely pointless.

We need a fuse that will blow if you short the 3V3 supply to ground, but also will sustain short-circuit current of both LDOs indefinitely. This needs measurement and experimentation...

@whitequark whitequark added revC Hardware revision: C and removed revB Hardware revision: B labels May 5, 2018
@awygle
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awygle commented May 5, 2018

Per IRC discussion, will use http://www.ti.com/lit/ds/symlink/tpd3s014.pdf instead.

@awygle awygle changed the title Use a polyfuse instead of a regular fast-blow fuse Use a dedicated USB protection IC instead of a regular fast-blow fuse May 5, 2018
@whitequark
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This seems simple enough we really should add this in revB.

@whitequark whitequark added revB Hardware revision: B and removed revC Hardware revision: C labels May 13, 2018
@whitequark whitequark added this to the Preview 1 milestone May 13, 2018
@whitequark whitequark mentioned this issue May 25, 2018
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@awygle
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awygle commented Jun 4, 2018

Closed by 369968e

@awygle awygle closed this as completed Jun 4, 2018
@whitequark whitequark added the hardware Component: hardware label Apr 16, 2019
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