F405 & F411 versions of the BluePill

What are you developing?
racemaniac
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Re: F405 & F411 versions of the BluePill

Post by racemaniac » Wed Dec 06, 2017 3:47 pm

Squonk42 wrote:
Wed Dec 06, 2017 3:29 pm
racemaniac wrote:
Wed Dec 06, 2017 3:11 pm
Maybe a diode like this: https://www.vishay.com/docs/88746/ss12.pdf
(also easily & cheaply found on aliexpress)
or a bit bigger & certainly capable of 1A: https://www.vishay.com/docs/88712/s2a.pdf
The first one has a Vf of 0.5V and is already 4 mm x 2.54 mm but may be acceptable with Tja of 88°C/W (44°C rise), the second has Vf of 1.15V and is even larger, so no way.

The MAX40200 ideal diode would match perfectly, but it is not cheap and cannot be found on Aliexpress:
MAX40200.png
Indeed, the bigger ones are too much, but those SS12 diodes may be an option? and they're indeed big, but if we can get some traces between its pads, it might work out? And it's also a cheap & easy to find diode, so ideal for the kind of board we're making.

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Wed Dec 06, 2017 3:56 pm

I agree, the SS12 is probably our only option, given the reduced board size. If we had more space, the RPi solution with P-MOSFET + current mirror is the cheapest and most efficient.

victor_pv
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Re: F405 & F411 versions of the BluePill

Post by victor_pv » Wed Dec 06, 2017 4:09 pm

Squonk42 wrote:
Wed Dec 06, 2017 3:45 pm
I am trying to understand how FET2 works in this schematic:
https://www.olimex.com/Products/Duino/A ... rev_A3.pdf
Seems like this circuit, this has the explanation on how it works. Called Q1 here:
https://behindthesciences.com/electroni ... y-circuit/

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Wed Dec 06, 2017 4:17 pm

OK, thanks, this is what I thought: it is only working if VUSB >> VBAT (at least by a diode drop), which is not the case for us (we have 5V on both sides). Nice trick, though!

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RogerClark
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Re: F405 & F411 versions of the BluePill

Post by RogerClark » Wed Dec 06, 2017 8:22 pm

Another thought about this...

The FET is basically just acting like a diode ( if it’s connected correctly ), and will handle the expected current.

But the issue is that sometimes the battery is allowed to feed the USB for OTG operation.

So can we connect the gate to a GPIO, and require software control for then using the battery connection ?
Possibly not, as for some time during startup the GPIO may not be the correct value?

Or alternatively, just directly connect VBAT , and users need to use their brains and not connect USB and battery at the same time. perhaps make the track very thin, to act like a fuse, so if the user does this, it burn the track but not the board..

Or use a jump link.

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Thu Dec 07, 2017 5:48 am

I updated the TODO list for the MOSFET problem.

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RogerClark
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Re: F405 & F411 versions of the BluePill

Post by RogerClark » Thu Dec 07, 2017 6:25 am

Is a 1N5817 OK

Looking on AliExpress there seems to be multiple vendors

Its 1A 20V

Edit.

I am changing my copy of the schematic now.

I've had to include the diodes library, but I guess now its in the schematic, I need to move the symbol into the board's custom lib.

I don't normally bother on components like diodes etc which are common, and only use custom libs for parts not available in KiCads default libs, but I can to manually add it to the boards on library, if we are happy with that diode

Edit.

Its a bit of a pain to do, but I've added a 1N5817 to the BluePill lib (in my local copy)

The diode prevents the +5V pin feeding the USB VBus

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Thu Dec 07, 2017 5:09 pm

We should stick to SMT components as much as possible to keep the price low.

SS12 diodes are extremely common, even on Aliexpress:
https://www.aliexpress.com/item/sku/32830718059.html

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RogerClark
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Re: F405 & F411 versions of the BluePill

Post by RogerClark » Thu Dec 07, 2017 7:55 pm

On Aliexpress they seem to be listed as SS12 1N5812 and as KiCad already has a symbol for a 1N5812 I thought I may as well use that if they are functionally equivalent.

However I don’t know what package the SS12 uses

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Squonk42
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Re: F405 & F411 versions of the BluePill

Post by Squonk42 » Thu Dec 07, 2017 9:35 pm

Sometimes Aliexpress vendors just add keywords in the title to catch attention.

SS12 are extremely standard SMD power diodes, they use an "SMA" (also called "DO-214AC") package, plenty of them on Digi-Key:
https://www.digikey.com/products/en/dis ... 280?k=ss12

AFAICT, it corresponds to the "D_SMA" footprint in the "Diodes_SMD" footprint library in Kicad. But in general I prefer to use my old trusted footprints rather than using an existing one that I have not checked against the real thing. One thing that makes me suspect problems is the "D_SMA_Handsoldering" variant...

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