CrazyMonkey
Member
This should be simple, but I am not sure.
I want to run my Maple (Rev5) from 3.3v.
I have several things that need 3.3v, and I don't want to have
two power supplies. I am not sure the maple can provide enough
power since its a linear regulator.
So, Id like to run everything off an external 3.3v source.
I am guessing I can't. Or would have to remove the regulators
on the board and do nasty things to make it work.
Anyone know?
robodude666
Member
Applying the 3.3v directly to VCC and VCCA will work, I'd imagine.
Worst case scenario is, depending on the current required, add a 3.3v to 5v boost converter which goes to the Maple's Vin and converted back to 3.3v.
Alternatively, use the Maple's 3.3v regulators to power your other devices.. It's very unlikely that you currently already have an exact 3.3v power source... It's most likely something different that you're regulating to 3.3v. If that's the case, let the Maple do it for you. You just supply something ~5v-12 to Vin, or a 3.7v Li-po battery to the battery input.
CrazyMonkey
Member
My device will be powered from 24v, So I have 3.3 and 5v buck converters.
I can use both, but id rather only use 1 (3.3) if possible. I also do not
think the maple can power all my other 3.3v stuff. I though about just
applying the 3.3 to the analog and digital pins, but I figured they were
outputs only. I guess I can unsolder the regulators to be sure it's safe
to do. Id rather leave them, so I can power if off usb for flashing.
(it would be disconnected from everything else when flashing).
I looked the the specs for the LDO linear regulators, but an still not
sure if applying power to the outputs with no input will harm them.
maybe I just have to remove the power selector jumper?
Is there a schematic for the maple v5?
Anyone done this and know its safe?
gbulmer
Moderator
CrazyMonkey - the schematics and PCB design files are in github.
This gives instructions to find them:
http://leaflabs.com/docs/hardware/maple.html#hardware-design-files
The schematic for r5 is at
https://github.com/leaflabs/maple/blob/master/maple-r5/maple-r5-schematic.pdf
The output of one regulator is connected to VDDA and the other to VCC.
Removing the power selector jumper will disconnect the inputs to the two regulators, but the outputs are still connected.
The least effort path sounds like powering the Maple from your 5V source, and the rest of the electronics from your 3.3V source. I think a Maple uses about 50mA when it isn't driving anything. The ADCs have their own supply (VDDA) to give slightly better quality measurements, which might be important to you.
(full disclosure: I am not a member of LeafLabs staff)
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