Max current out of 3V3?

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mathieu
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Max current out of 3V3?

Post by mathieu » Thu Nov 19, 2020 10:26 pm

I feel like this question must be answered somewhere, but I've been looking for some time now with no success: what is the max current that can be safely supplied by each of the 3V3 pins of the pyboard 1.1?

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jimmo
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Re: Max current out of 3V3?

Post by jimmo » Thu Nov 19, 2020 10:37 pm

mathieu wrote:
Thu Nov 19, 2020 10:26 pm
I feel like this question must be answered somewhere, but I've been looking for some time now with no success: what is the max current that can be safely supplied by each of the 3V3 pins of the pyboard 1.1?
Hi,
Are you asking how much current can each of the GPIO pins source, or the 3.3 power pins?

The GPIO pins can source (and sink) 25mA each and a combined total of ~240mA (See https://www.st.com/resource/en/datasheet/dm00037051.pdf)

On the v1.1, the 3.3V power pins all share the same regulator (which is also used by everything on the board) which can supply 250mA. (See https://store.micropython.org/product/PYBv1.1)

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pythoncoder
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Re: Max current out of 3V3?

Post by pythoncoder » Fri Nov 20, 2020 8:17 am

jimmo wrote:
Thu Nov 19, 2020 10:37 pm
...
On the v1.1, the 3.3V power pins all share the same regulator (which is also used by everything on the board) which can supply 250mA. (See https://store.micropython.org/product/PYBv1.1)
This statement needs some qualification.

The spec says "capable of supplying up to 250mA, input voltage range 3.6V to 16V ". The 3V3 regulator is a linear device sourced from V+. If V+ is 5V then a current of 250mA looks feasible, with the regulator dissipating (5 - 3.3)*0.25 = 0.425W. At the other extreme, with Vin == 16V, available current will be much less.

Calculating a worst-case figure is a little involved as it involves thermal issues but you can be sure the regulator would go into thermal protection under those conditions.
Peter Hinch

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jimmo
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Re: Max current out of 3V3?

Post by jimmo » Fri Nov 20, 2020 12:33 pm

pythoncoder wrote:
Fri Nov 20, 2020 8:17 am
This statement needs some qualification.

The spec says "capable of supplying up to 250mA, input voltage range 3.6V to 16V ". The 3V3 regulator is a linear device sourced from V+. If V+ is 5V then a current of 250mA looks feasible, with the regulator dissipating (5 - 3.3)*0.25 = 0.425W. At the other extreme, with Vin == 16V, available current will be much less.

Calculating a worst-case figure is a little involved as it involves thermal issues but you can be sure the regulator would go into thermal protection under those conditions.
This is a very important qualification. Thanks Peter!

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