How to build a very low quiescent current 1.4V LDO

Thread Starter

praondevou

Joined Jul 9, 2011
2,942
Hi,

First of all, Happy New Year to everybody!! Hope you are doing good.

Now my problem:
I want to power a microphone with a button cell. The button cell is a silver oxide one with an initial voltage of 1.55V (new).
The microphone works down to 0.9V, it's maximum rating is 1.45V though. The microphone consumes not more than 25uA. I want to limit the voltage on the microphone to 1.4V max without adding more than a few uA (< 10). I know it can be done with a comparator and voltage reference and P-FET but current will be higher than just a few uA due to the voltage reference AND the component count is quite high.

Just putting a schottky in series will not allow me to completely discharge the battery, unfortunately discharge curves for that battery available on the internet vary widely also, some are straight at about 1.3V, some decrease almost linearily...

Any ideas? Low component count, low additional current, 1.35 to 1.4V maximum output voltage. Ideally I would remove 0.15V when the battery is new and once it arrives at 1.4V it just goes straight through to the load (microphone)

Thanks

Link to datasheet: http://store.invensense.com/datasheets/invensense/ICS-40310_ProductSpec_V1 0.pdf
 

crutschow

Joined Mar 14, 2008
23,742
A small Schottky diode in series should work for you.
A simulation of one is shown below.
All the silver oxide battery curves I've seen have a relatively flat output voltage as they discharge, so the amount of battery capacity left should be quite small after it drops to below the operating point of the amplifier with the diode in series.

I don't know of any low current, low voltage circuit that will do what you want.

Diode.PNG
 

Thread Starter

praondevou

Joined Jul 9, 2011
2,942
Hi Crutschow,
Thanks for taking the time to respond. After having a closer look at the various discharge curves I think you are right. I would probably be able to use 80 to 85% of the battery capacity. I will try it out.

Thanks
 

hp1729

Joined Nov 23, 2015
2,304
Hi,

First of all, Happy New Year to everybody!! Hope you are doing good.

Now my problem:
I want to power a microphone with a button cell. The button cell is a silver oxide one with an initial voltage of 1.55V (new).
The microphone works down to 0.9V, it's maximum rating is 1.45V though. The microphone consumes not more than 25uA. I want to limit the voltage on the microphone to 1.4V max without adding more than a few uA (< 10). I know it can be done with a comparator and voltage reference and P-FET but current will be higher than just a few uA due to the voltage reference AND the component count is quite high.

Just putting a schottky in series will not allow me to completely discharge the battery, unfortunately discharge curves for that battery available on the internet vary widely also, some are straight at about 1.3V, some decrease almost linearily...

Any ideas? Low component count, low additional current, 1.35 to 1.4V maximum output voltage. Ideally I would remove 0.15V when the battery is new and once it arrives at 1.4V it just goes straight through to the load (microphone)

Thanks

Link to datasheet: http://store.invensense.com/datasheets/invensense/ICS-40310_ProductSpec_V1 0.pdf
There must be something for me to learn here. Why power the microphone separately instead of from the circuit it goes to?
 

Thread Starter

praondevou

Joined Jul 9, 2011
2,942
"The rest of the circuit" could support way more than 1.55V. The problem is the initial voltage of the battery cell which is higher than the maximum rating of the microphone.
 
Last edited:

Dodgydave

Joined Jun 22, 2012
8,571
So why not power the microphone from the circuit psu, and use an lm317 to drop the voltage to 1.5v, or use two silicon diodes as a voltage regulator?
 

Thread Starter

praondevou

Joined Jul 9, 2011
2,942
So why not power the microphone from the circuit psu, and use an lm317 to drop the voltage to 1.5v, or use two silicon diodes as a voltage regulator?

The whole circuit is powered by the button cell but only the the microphone has a maximum rating of 1.45V, which I do not want to exceed.

And a LM317 has a minimum load current requirement of 3.5mA.

Anyway, I made a practical test and yes, a schottky diode (I used the BAT54) does the job, voltage remains just below 1.45V, tested from 6uA to 31uA. Need to do this at different temperatures now. I was confused about the many different discharge curves...

Thanks all
 

GopherT

Joined Nov 23, 2012
8,012
Hi,

First of all, Happy New Year to everybody!! Hope you are doing good.

Now my problem:
I want to power a microphone with a button cell. The button cell is a silver oxide one with an initial voltage of 1.55V (new).
The microphone works down to 0.9V, it's maximum rating is 1.45V though. The microphone consumes not more than 25uA. I want to limit the voltage on the microphone to 1.4V max without adding more than a few uA (< 10). I know it can be done with a comparator and voltage reference and P-FET but current will be higher than just a few uA due to the voltage reference AND the component count is quite high.

Just putting a schottky in series will not allow me to completely discharge the battery, unfortunately discharge curves for that battery available on the internet vary widely also, some are straight at about 1.3V, some decrease almost linearily...

Any ideas? Low component count, low additional current, 1.35 to 1.4V maximum output voltage. Ideally I would remove 0.15V when the battery is new and once it arrives at 1.4V it just goes straight through to the load (microphone)

Thanks

Link to datasheet: http://store.invensense.com/datasheets/invensense/ICS-40310_ProductSpec_V1 0.pdf
A working voltage range of 0.9 to 1.45V seems like this device was designed around a one-cell niCad battery instead of silver oxide technology.

Here is the voltage discharge curve for NiCd. Max is 1.4 (typically 1.35) and end of life is typically considered 1.1.

image.jpg
 

Thread Starter

praondevou

Joined Jul 9, 2011
2,942
A working voltage range of 0.9 to 1.45V seems like this device was designed around a one-cell niCad battery instead of silver oxide technology.

Here is the voltage discharge curve for NiCd. Max is 1.4 (typically 1.35) and end of life is typically considered 1.1.

View attachment 97971
Interesting!! The problem is the battery size though, I want to use a 335 button cell which is the thinnest small diameter battery I could find...
 
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