What is the minimum current necessary for an ADC to read a voltage?

MichaelL65
Posts: 1
Joined: Thu Nov 02, 2017 9:50 pm

What is the minimum current necessary for an ADC to read a voltage?

Postby MichaelL65 » Thu Nov 02, 2017 10:34 pm

I'm working on a circuit that requires monitoring of the battery level, but the battery needs to last as long as possible. I'm planning to use a regulator to run the ESP32 on 3.3V, and I'm having it look at a voltage divider on the actual battery level (so I'm always looking at a voltage that is half of the battery, which will always be less than 3.3V).

Because I want to keep this as low current as possible, what is the MINIMUM current that needs to be available on the ADC pins for it to read? For example: If I use two 100K resistors for the voltage divider across a 4.5V battery, it will draw only 22.5µA on the battery. But would that still be enough for the pin to be able to read the value? (I'm assuming there needs to be SOME current)

I have looked through several of the data sheets, but I can't seem to find that answer. Can someone help me?

big819
Posts: 1
Joined: Sat Aug 18, 2018 8:45 pm

Re: What is the minimum current necessary for an ADC to read a voltage?

Postby big819 » Sat Aug 18, 2018 8:48 pm

have you found any new information on this? I am also looking for a reliable way to do a voltage reading on battery.

mikemoy
Posts: 599
Joined: Fri Jan 12, 2018 9:10 pm

Re: What is the minimum current necessary for an ADC to read a voltage?

Postby mikemoy » Sun Aug 19, 2018 4:34 am

I dont know the answer to this, but why not just try it ?
Keep increasing your divider values until it starts to be incorrect.

JoaoLopesF
Posts: 59
Joined: Thu Aug 17, 2017 5:40 pm

Re: What is the minimum current necessary for an ADC to read a voltage?

Postby JoaoLopesF » Sun Aug 19, 2018 3:16 pm

Hi @MichaelL65

In my tests, the reliable maximum values of resistor divider of VBAT is 68k/33k .
But it still drop power of battery.

Now in my projects, I ground the divider only when I need read the ADC value.
It is done by a another GPIO, and can be plugged a MOSFET N-Channel (HIGH to read) or direct on divider (LOW to read).
And before enter in deep-sleep, I unground this.
In my tests, the ESP32 sustain the state of GPIO in deep sleep, and no have consupmition of battery.

I just made a set of examples of BLE connected devices with mobile apps.
And It support a battery powered devices.

You can see the sugested schematics on https://github.com/JoaoLopesF/Esp-Idf-M ... schematics

I hope helped You.

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