Replace AMS1117 5V-3.3V LDO on NodeMCU for LiPo with low quiescent current

Question

I want use my NodeMCU to drive a SIM808 Module with integrated LiPo Charger. https://www.itead.cc/wiki/SIM808_GSM/GPRS/GPS_Module

There are two problems. First of all the SIM808 Module just provides the LiPo Voltage, no steady 3.3V or 5V output. The NodeMCU needs 3.3V (or 5V with LDO). The internal LDO has a high quiescent current of >1mA. So the idea would be to replace the onboard 5V to 3.3V LDO with one with a low quiescent current (<0.1mA) for direct LiPo input (3.7-4.3V) and 3.3V output which is pin compatible to just replace it direcly on the NodeMCU.

The MCP1700 would be an option as TO92 to make the PINs fit because VIN/VOUT is reversed.

This would be my easiest idea. Do you have any different ideas?

More about the NodeMCU and the AMS1117 position on the board https://tinker.yeoman.com.au/2016/05/29/running-nodemcu-on-a-battery-esp8266-low-power-consumption-revisited/

Answer 1

You choice looks good to me, but only if your NodeMCU is going to spend most of its time sleeping. In that case I'd use a MCP1700 (quiescent current < 4 uA).

If it's going to spend a significant % of time up and running you may be better off using a switching regulator. It's all about considering the energy saved when it's sleeping vs. the energy saved when it's operating.

Answer 2

FYI, the Diodes Inc AP7361C-33ER has the same pin-out, 1A current capacity, 360mV drop-out (so can generally be used with LiPo), 60uA Iq (pretty good for a 1A LDO). $0.62 qty1 in stock at Digikey. There are many other choices in LDOs but very few that are pin-compatible and have high current capacity, e.g., the MCP1700 is 250mA in comparison. Of course it all depends on what you need...