Question about power supply

[Gregwar]

Hello,

I'm wondering about power supply

You says that this board can be supplied with a range of 3V to 12V, but the regulator on the board have a dropout of 625mV, so it is not supposed to work with less than 3.925V, right?

[poslathian]

That is a good question. The linear regulators definitely have a
drop-out - although I have measured it to be a bit lower than that spec.

In any case, the STM32 processor will happily operate with Vcc down to
2.5. You will probably notice the LED stops flashing under 2.8 or so.

Older versions of Maple Mini (r1) have an additional .2V diode drop on Vin.

However, I do think the note in the documentation needs to be updated.
Thanks for pointing it out!

Also note, that since these are linear regulators, the maximum voltage
is dependent on total power draw. If you are using lots of GPIOs to
drive LED's and such, it is safest to stick with 5V.

Andrew

[poslathian]

Gregoire,

That is a good question. The linear regulators definitely have a
drop-out - although I have measured it to be a bit lower than that spec.

In any case, the STM32 processor will happily operate with Vcc down to
2.5. You will probably notice the LED stops flashing under 2.8 or so.

Older versions of Maple Mini (r1) have an additional .2V diode drop on Vin.

However, I do think the note in the documentation needs to be updated.
Thanks for pointing it out!

Also note, that since these are linear regulators, the maximum voltage
is dependent on total power draw. If you are using lots of GPIOs to
drive LED's and such, it is safest to stick with 5V.

Andrew

On 08/22/2013 04:27 AM, Grégoire Passault wrote:

Hello,

I'm wondering about power supply

You says that this board can be supplied with a range of 3V to 12V, but
the regulator on the board have a dropout of 625mV, so it is not
supposed to work with less than 3.925V, right?

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[Gregwar]

Thanks for the reply

In the documentation the range should indeed be 4.0 - 12V OR 3.3V (if you supply directly Vcc)
And this should also be explained here:

"If you are planning to draw a lot of current from the Maple board, it is necessary to provide input power as close to 3.3V as possible."
-> Yes, but in this case I guess I should not use VIN but VCC, because VIN will lead to a 2.7V power supply with a good 3.3V input

And thanks for this great board, it a really nice and powerful tool