Espruino JavaScript
Powering Pico with a 3V lithium battery #5463
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Posted at 2016-10-14 by @allObjects Pico chip chip STM32F401CDU6 6.3.1 General operating conditions - p. 60 - and Table 15. Posted at 2016-10-14 by GeekBot Thank you allObjects, looking at the schematics, as you say, we see that the 3.3V regulator output is connected on the 3.3V pin. I will have a look at the regulator datasheet to see whether it accepts 3.3V external feeding on the output or not. May be somebody else knows... Posted at 2016-10-14 by GeekBot Looking at the datasheet, it seems possible. However, a resistor bridge at the output will probably consume some current. No idea how much. Posted at 2016-10-14 by @gfwilliams It won't hurt to try at all (as long as you don't put the battery in backwards :) ). I've literally just got some Lithium batteries (1/2 AA cell) this week. Having tried it out, you can connect to the 'Bat' pin quite happily. At low power draws (~20mA or so?) the voltage drop across the regulator is very low (0.02v when I measured at 10mA). Since the Pico will operate down to 1.7v you'd be able to flatten a CR2450 without much trouble. Powering via the 3.3v rail would also be fine and would avoid the regulator's voltage drop, but you then couldn't use USB or you'd end up putting 3.3v on the battery and charging it Posted at 2016-10-14 by GeekBot Thank you Gordon for these good news, that is very clear. Posted at 2016-10-16 by GeekBot @gfwilliams, eventually I have a doubt; the 'Bat' pin you talk about is the 'VBat' pin (PIN2 of J2 on Pico, called 5V on the schematic) ? Posted at 2016-10-17 by @gfwilliams It's the Pin 1 - Unfortunately the pin naming is a bit confusing. The other pin will have 5v on it when USB is connected, so you definitely don't want to put the lithium battery on that :) Posted at 2016-10-17 by GeekBot Thank you Gordon. So I connected on BAT_IN as you suggest, it's clearly much safer and easier to manage with USB connection. The voltage drop is about 0.3 V. That's 10% of the battery voltage, but acceptable for my application. I guess this drop comes from the MOS transistor? Posted at 2016-10-17 by @gfwilliams Where are you measuring the voltage drop? The FET shouldn't really drop any noticeable voltage. It could be from the voltage regulator, but when I measured there was very little voltage dropped. Are you powering something else as well that might be drawing a bit of current? Posted at 2016-10-18 by GeekBot @gfwilliams, thank you, I will do accurate measurements and reporting tomorrow. I come back to you. Posted at 2016-10-22 by GeekBot I did some more measurements. |
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Posted at 2016-10-14 by GeekBot
Hello
I want to power my Espruino Pico with a Lithium battery CR 2450 (3V and probably down to 2.5 V). I read the doc on powering, and I see that Vbat should be > 3.6 V.
Is it possible to power Pico with a 3V Lithium battery ?
On which Espruino pin shall I connect the + of the battery ?
Thanks a lot
GeekBot
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