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I have a MCU that powers up periodically to log some data and then powers down (full power off -- not sleep). When powered on, it runs off a battery and I want to connect the battery to an analog pin on the MCU to measure its voltage, but I don't want it to backpower my MCU when it is powered off.

Is there a recommended type of component that I could use to effectively isolate the MCU from the battery when the MCU is off? This would need to work without interfering with the voltage value being read by the analog pin.

I was thinking about possibly using an analog switch IC like: https://www.ti.com/lit/ds/symlink/tmux1101.pdf

I once used a similar 2 channel IC for isolating I2C with good results: https://www.ti.com/lit/ds/symlink/ts5a23159.pdf

Wondering if this is a reasonable solution or if I should consider other options? I'm an EE hobbyist, not anywhere close to an expert. Thanks.

Update: Thanks to @DKNguyen for pointing me to an existing answer that was for a different but similar problem that requires the same solution: Low current battery monitoring

I implemented this solution and can confirm that it works.

kr4sh
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  • how would you measure the voltage with a powered off MCU? – jsotola Nov 04 '21 at 05:33
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    Search on this stack exchange. Someone has asked this before and it has been answered. It was very similar but not exactly the same concern, but same solution either way. I think it was about disconnecting a resistive divider used to measure battery voltage so the divider would not always be draining the battery while the MCU was in sleep. – DKNguyen Nov 04 '21 at 05:46
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    https://electronics.stackexchange.com/questions/64490/low-current-battery-monitoring – DKNguyen Nov 04 '21 at 05:51
  • https://electronics.stackexchange.com/questions/343435/low-power-battery-voltage-monitor – DKNguyen Nov 04 '21 at 05:52
  • kr4sh - Hi, Since you've kindly updated that an existing answer solved your problem, I'll close your question as a duplicate of that one. Thanks. – SamGibson Dec 03 '21 at 06:27

2 Answers2

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This is from LT8490 datasheet. Your point of interest is the dotted circuit, that disconnects the resistor divider:

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SamGibson
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Marko Buršič
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Use a p-MOSFET in series between VDD and the first resistor of the voltage divider. I mean the high side resistor.

Control the p-MOSFET by a digital pin of your MCU.

Enrico Migliore
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