Author Topic: bypassing Moteino regulator rises current draw  (Read 996 times)

hakunin

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bypassing Moteino regulator rises current draw
« on: March 30, 2017, 06:00:35 PM »
Hi,
I have a Moteino R4 with RFM69W.  If I connect my 3.3V regulated power source to the VIN pin of Moteino, I get 6.5uA during sleep. If I bypass the Moteiono regulator and connect directly to 3v3 pin, I get 1.41 mA, same code.
The multimeter is between V_out of my power source and Moteino VIN or 3V3 pin.
There are no other devices or cables in the circuit. The code is just delay 4 secs and sleep 4 secs (RocketStream LowPower Library and LowPowerLab RFM69 lib).
I've looked on Moteino schematics but I am not sure about the cause. I've tested two Moteinos.
Has anybody an idea?
Thanks for your help
Sincerely

perky

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Re: bypassing Moteino regulator rises current draw
« Reply #1 on: March 30, 2017, 06:33:00 PM »
By 'bypass' do you mean completely remove? Or do you mean just connecting to 3.3V with the regulator still connected? The latter is likely to cause excessive current.

Mark.

hakunin

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Re: bypassing Moteino regulator rises current draw
« Reply #2 on: March 30, 2017, 07:03:49 PM »
Hi Mark,
thanks for your help. With bypassing I meant connecting to 3v3 without removing the regulator, sorry for the confusion. Why would this cause excessive current?

perky

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Re: bypassing Moteino regulator rises current draw
« Reply #3 on: March 31, 2017, 07:12:26 AM »
Applying 3.3V to the output of the regulator means the diode in the pass FET in the regulator gets forward biased, and therefore 3.3V minus a voltage drop appears on VIN. That in turn powers the regulator, but that regulator isn't really suited to having it's VIN less than its VOUT and takes more quiescent current. The current you're getting does seem a little high for that I have to say, but the regulator is operating outside of its normal working mode so all bets are off as to what you'll get. So you should at least isolate the 3.3V output from the regulator, either by taking it off completely or some other method.

Mark.
« Last Edit: March 31, 2017, 07:15:24 AM by perky »

hakunin

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Re: bypassing Moteino regulator rises current draw
« Reply #4 on: March 31, 2017, 05:37:28 PM »
Mark,
thank you so much! I didn't know this and your advice is really helpful for my projects!
Thanks
Sincerely