very small STM32F405 board

Any other STM32 based boards
zmemw16
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Re: very small STM32F405 board

Post by zmemw16 » Fri Jul 28, 2017 11:43 pm

ag123 wrote:
Fri Jul 28, 2017 4:40 pm
this may somehow mean that if there is some ways to 'heatsink' that sot23 LDO, we may literally reduce the thermal resistance (and possibly significantly), this could for instance be possible by using some heatsink thermal compounds, but it would also mean attaching a heatsink so that all that heat is conducted away and dissipated over a (much) larger area.
increasing the pcb copper area for the LDO is not possible.
cringe if you wish, lift the tab insert copper plate and resolder both to original copper pad :lol:

otherwise lift the LDO and use 3 wires to another regulator with a heatsink appropriately mounted
srp

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Pito
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Re: very small STM32F405 board

Post by Pito » Sat Jul 29, 2017 9:40 am

Simple Pito's 9193 cooler:
Take a piece of wire, ie. 0.4-0.6mm dia, make a small coil from it, say 4-5windings 2mm dia, solder the short leads to pins 1 and 3 (Vin, En) such the coil touches the top of the package. Apply a small dot of glue or (none conducting) thermal paste beneath the coil such it gets better thermal contact to the package. It will cool down the chip via pins 1 and 3 as well as via the top of the package. Not to scale:
9193 cooler.JPG
9193 cooler.JPG (14.8 KiB) Viewed 241 times
No warranties of any kind, use at your own risk :)
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Ollie
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Re: very small STM32F405 board

Post by Ollie » Sat Jul 29, 2017 4:05 pm

In addition to these numeric calculations, I do wonder if anybody has done thermal imaging of F103 and F407 boards to determine if this is a real problem.

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Pito
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Re: very small STM32F405 board

Post by Pito » Sun Jul 30, 2017 11:43 am

Not having the infra thermometer handy, I loaded BPill's 3.3V rail with 33ohm (5V from USB as the input), so the Iout was maybe 120mA, the temperature of RT's package (the finger method) was below 50degC (you can keep touching with your finger till about 50degC with a standard human).

With 2x 33ohm in parallel the Iout aprox 220mA, and you cannot touch the package anymore, crazy hot!

Would be great if somebody could measure the temperatures and verify the tables above.

Btw, the fundamental laws of physics are not easy to bypass as of today, the thermal power dissipated by any linear voltage regulator is simply

P = (Uin - Uout) * (Iout + Ireg), [W, V, A], where Ireg could be neglected with modern regs.
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ahull
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Re: very small STM32F405 board

Post by ahull » Sun Jul 30, 2017 1:15 pm

Pito wrote:
Sun Jul 30, 2017 11:43 am

...you can keep touching with your finger till about 50degC with a standard human...
That is for a metric calibrated human finger. Those of you in the land of Trumpentweet will have fingers pre-calibrated to 122 F ;)
- Andy Hull -

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Pito
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Re: very small STM32F405 board

Post by Pito » Sun Jul 30, 2017 1:24 pm

Yes, degC as degree Celsius.. (0degC - pure water freezes, 100degC pure water boils, at the sea level) :)
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victor_pv
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Re: very small STM32F405 board

Post by victor_pv » Sun Jul 30, 2017 1:28 pm

ahull wrote:
Sun Jul 30, 2017 1:15 pm
Pito wrote:
Sun Jul 30, 2017 11:43 am

...you can keep touching with your finger till about 50degC with a standard human...
That is for a metric calibrated human finger. Those of you in the land of Trumpentweet will have fingers pre-calibrated to 122 F ;)
Those of us have such a thick skin by now that our fingers will probably burn before we notice...

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ahull
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Re: very small STM32F405 board

Post by ahull » Sun Jul 30, 2017 2:07 pm

victor_pv wrote:
Sun Jul 30, 2017 1:28 pm
ahull wrote:
Sun Jul 30, 2017 1:15 pm
Pito wrote:
Sun Jul 30, 2017 11:43 am

...you can keep touching with your finger till about 50degC with a standard human...
That is for a metric calibrated human finger. Those of you in the land of Trumpentweet will have fingers pre-calibrated to 122 F ;)
Those of us have such a thick skin by now that our fingers will probably burn before we notice...
.. in which case, a keen sense of smell will be needed to determine if the finger is rare, medium or well done.
- Andy Hull -

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Pito
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Re: very small STM32F405 board

Post by Pito » Sun Jul 30, 2017 2:17 pm

For people with thick skin and a limited sense for smell there is an another test - the spit test.
Spit at the voltage regulator, and when
- the water boils and evaporates within 3 seconds - the temp is >= 110degC
- you see dancing balls - the temp is >= 210degC

You also may spit at your finger and when it sizzles when touching the regulator the temp will be >=110degC.
The people with musical ear may distinguish the temperature ranges based on the sizzle's pitch :)

Use at your own risk, no warranties of any kind..
:) :)
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Ollie
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Re: very small STM32F405 board

Post by Ollie » Sun Jul 30, 2017 4:25 pm

This is starting to get funny

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