Hi,
I currently also work on a new circuit design to further reduce the power consumption of my battery powered moteino. I plan to do something similar with Toms circuit a few replies above.
I understood your posts in that why, that a more or less constant current consumption results in better battery life than current peaks caused by the Listening Mode or frequently transmissions.
--> So, the target is to make the current consumption as smooth as possible with a well defined cap, which buffers the transmissions and listening mode current peaks?
What do you think about using the IRLML6402 Mosfet instead of SI2365? (No supplier is available which makes sense for me)
It has a very low on resistance and should work with 3.3V on/off.
http://www.irf.com/product-info/datasheets/data/irlml6402.pdf
Am I right?
Assuming your power supply is at least 3V, then, yes, that MOSFET will be fine. It's too bad the data sheet doesn't show the drain current vs Vgs at lower currents, but it appears to be more than enough for this application.
If you can fit a larger cap than I used, it would be much much better. 200uF is really not enough to isolate the pulsed load from the battery and I can see 40mA spikes at the battery when the RFM69W is transmitting at full power (my code automatically dials back the transmit level, but this is the worst case condition).
In the scope trace below, you can see the blue trace is the CR2032 which starts at 3.0V but then falls to about 2.4V during the transmit (and recovery) time while the yellow trace is across the 200uF cap & RFM69W falls below 2.0V. The purple trace is the difference of the two voltages across a 10 ohm resistor, 400mV or 40mA. It's brief and the battery recovers quickly, but if you can use a supercap or, at least, something substantially larger than 200uF you'd be better off. Of course, I'm using the same coin cell that I've been abusing for weeks so I'm not sure how a fresh one will behave. This one keeps on working and I'll keep abusing it until it stops
In any case, I'm happy with the circuit and have sent it to OSH Park for fab. I'll let you know (and post the design files) when I have the PCB running (probably within two weeks).
Tom