Feel there should be an easy answer to this. I'm looking to shave about 0.6V off a battery source voltage to get it from 4.2V to 3.6V. The 3.6V is being used to run the backup domain power of a micro controller. I'd like to avoid voltage dividers or LDO regulators to keep the "backup" current draw to an absolute minimum. My first attempt involved just dropping a couple of diodes in series after the 4.2V, but at the minuscule currents that the backup domain draws (3-4 uA) the forward drop of the diodes I've tried is negligible. Anyone have any thoughts?
TIA
Jon
Micropower LDO regulator is the easy answer I suspect.
Could a zener work for that?
I Googled "low leakage diode", and got diodes with >0.5volt drop at 1uA.
Leo..
All diodes have the same basic behaviour of ~60mV per decade of current, so given a requirement
to work at both a few uA and at full load current you still get a similar shift in voltage, whatever
diode - the offset will vary depending on the bandgap and area of the junction (which sets the current
density).
The ultra-low leakage diode is probably just a smaller die so the current density is much higher than in
standard diodes for a given external current, so the forward voltage is higher.
Of course the leakage current is less because the leakage current density is multiplied by a
much smaller active device area.
Have you tried a series resistor to drop the voltage.
LarryD:
Have you tried a series resistor to drop the voltage.
Have you really read the question?
Yes
I wanted to find out if it would work.
I wasn't suggesting it would be his solution.
Perhaps an adjustable, low dropout, micropower reference set to 3.6V would work.
4µA quiescent current, source 10mA, sink 2mA. LTC1798 Series
I tried with Zener. It's working.
Now measure your current draw at the battery.
A zener is a shunt regulator, so much current is wasted to regulate the voltage.