<Twix>
i didn't see an usb host really limiting the current to 500 mA since a long time. My notebook delivers 3.5 A on all ports. Even 5.3 A on one of the ports(are the USB connectors even rated for that abuse?)
<Twix>
But i would agree, that it should be ok to not solder the thermal pad. Its only feeding the fpga core(and pll) voltage, it usually does not take much
<Twix>
And i would assume that the regulator would protect itself from overheating, as those things usually do
<sorear>
I'm saying 500 mA because there's a current limiter chip on glasgow itself
<sorear>
upstream of the regs
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<whitequark>
martinr: it doesn't dissipate any noticeable power
<whitequark>
the current draw on it is less than a milliamp
<whitequark>
hey folks
<electronic_eel_>
the 1v2 rail needs less than a milliamp?
<whitequark>
do y'all encounter charging-only USB cables a lot? i do and i find it infuriating. what do you think about adding a feature where if FX2 has power but no USB link it would aggressively blink?
<whitequark>
electronic_eel_: yeah, i think we have that on schematic?
<whitequark>
ok sorry, with hx8k it's 1.14 mA
<whitequark>
hm
<whitequark>
actually, now that you mention it, it's not quite that simple
<whitequark>
1.14 mA is the static current, 22.3 mA is the startup supply current
<whitequark>
but it doesn't actually say anywhere what the maximum current is, I guess that can only be extracted from a design
<electronic_eel_>
yes, that sounds more reasonable. it depends on how many gates switch at once
<whitequark>
indeed
<electronic_eel_>
but it is still low compared to other fpgas, so no special heatsinking required on the regulator
<electronic_eel_>
re your blink-on-no-usb idea: what about if you loaded a bitstream into the eeprom and want to run glasgow standalone with it?
<whitequark>
maybe only if there's no bitstream?
<d1b2>
<daveshah> Yeah the theoretical maximum current - every LUT, wire and FF switching at say 400MHz or whatever the limit is will be quite high
<tnt>
So 1 data point is 3000FF in a UP5k toggling every cycle at 82.5 MHz was ~30 mA if memory serve.
<d1b2>
<daveshah> I would guess that means the maximum theoretical for hx8k would be O(200mA) then
<d1b2>
<daveshah> But thats nowhere near any realistic design which will have an activity factor on all the FFs
<electronic_eel_>
tnt: wow, that is still quite low. i would have guessed more
<tnt>
electronic_eel_: yeah, it's some old measurements I made because on my first ice40 board, not knowing what to expect, I put a 1.5A SMPS for the vcore :)
<d1b2>
<daveshah> Hehe, 1.5A is plenty even for most ECP5 85k designs
<electronic_eel_>
hehe, that seems very oversized in retrospect
<electronic_eel_>
whitequark: which led do you suggest to blink? error?
<whitequark>
maybe FX2?
<whitequark>
or FX2+ERR
<whitequark>
i guess blinking just FX2 makes sense in a way because it's like if FX2 is "pending"
<whitequark>
(waiting for the link)
<whitequark>
ultimately people would still have to look up the exact meaning, but this one seems easier to remember
<whitequark>
and if there's a bitstream, it will light up "ICE"
<electronic_eel_>
yes, i think that makes sense. blinking err seems a bit aggressive
<whitequark>
so it's as if it booted to that phase
<whitequark>
yep
<whitequark>
now, i am actually not sure how to detect USB link presence
<whitequark>
ah, can probably check if an address is assigned
<electronic_eel_>
then maybe my suggestion of not doing it when you have a bitstream in eeprom is not so good, because it complicates the states for the user
<whitequark>
true
<electronic_eel_>
i thought more about blinking err when writing that, but when we blink fx2 i think it is ok
<d1b2>
<theorbtwo> I mean, unless you are doing it in hard hardware, it's not like it's impossible to override it if you are making something where you are using a Glasgow with no usb link on purpose.
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<whitequark>
does anyone want to check what happens when our TPD3S014 gets 20V on input?
<whitequark>
there are some type-C chargers that just always have 20V on Vbus
<d1b2>
<Attie> oof...
<apo>
WCGW
<apo>
(You didn't need that phone anyway, right?)
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<electronic_eel>
whitequark: you are sure this is called a "charger"? "usb destroyer" seems a more fitting name to me
<whitequark>
electronic_eel: look, i was opposed to using the type-C connector...
<whitequark>
and now that i have experience using it, i am like 2.5 times more opposed to it
<electronic_eel>
what happens when you plug it into glasgow will probably depend on how the overcurrent limiting is designed in this "charger"
<whitequark>
electronic_eel: it drops the voltage until the current is within its capacity
<electronic_eel>
actual current limiting and no hiccup?
<whitequark>
so assuming there's a TVS in TPD3S014 that triggers at slightly above 5V, it's going to plow several amps at that threshold voltage into TPD3S until the latter dies
<whitequark>
yes, I asked the person with hands-on experience with this excuse of a charger
<whitequark>
there is a reason every PD controller worth its salt protects from 20V on every single line, even if the device never needs anything more than 5V
<electronic_eel>
if it is actual current limiting, then the TPD3S014 will die
<whitequark>
yep
<DX-MON>
surely you mean "walking spec violation"? :P but fair
<whitequark>
but I'm curious whether it will die closed or die open
<whitequark>
if the latter, changing the TPD3S is a dollar plus rework. if the former, you're out $130
<electronic_eel>
probably die shorted, that is the most common failure mode for tvs. but it is of course not guaranteed and if you do this like a hundred times, some will probably also die open
<whitequark>
is anyone here willing to get a dozen TPD3S and destroy them in the name of science?
<whitequark>
I would do it myself but getting anything from Mouser is an entire endeavour
<whitequark>
and none of the importers I checked have any in stock
<electronic_eel>
hmm, i'm not sure a test like this is very helpful, because it will only tell us what happens with this exact "charger"
<electronic_eel>
the outcome will probably depend on stuff like current regulation speed and output capacitance
<whitequark>
ah, i see
<electronic_eel>
also if you plug it into mains and then glasgow or first glasgow and then mains
<tnt>
I'm not really sure why you'd expect "current regulation" from that charger.
<whitequark>
tnt: like I said, that's observed behavior
<whitequark>
who knows why they made it that way
<whitequark>
outbreak of batshit insanity in some ODM's design department?
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<whitequark>
I kinda wish there was a device that's a cross between TPD3S014 and TPD4S014
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