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I'm setting up a power regulation system for a lithium polymer battery, but I'm aware that my LDO will continue to draw current from the battery even after it's fallen below an acceptable level of charge.

Is there anything I can do to shutdown my LDO after a certain input voltage?

My understanding is that it will continue to draw current, but output a lower voltage until it cuts out around 2.5V, which is much lower than the battery voltage should go.

I'm using a MCP73831 Battery management IC with the LD3985M33R LDO.

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The LDO regulator has an inhibit input so use a small voltage comparator looking at the Li-ion battery terminal voltage and when it drops to a certain low level, have the comparator switch so that the LDO Reg turns off via the inhibit input. It's called UVLO (under-voltage lock-out) by quite a few chip suppliers.

You might be able to use that inhibit input directly but it's got a fair amount of hysteresis - to turn the device off requires an input that is below 0.4V and to restore it to full working it seems it needs 1.2 volts.

Also, check that the current draw from the inhibited regulator is low enough not to worry a Li-ion battery that is close to its lower discharge point. If the inhibited current is still fairly significant then you may need to use a MOSFET between battery and regulator.

Or, maybe change your scheme to use a regulator with UVLO built-in: -

enter image description here

The LTC3129 is a buck-boost regulator so even if the input voltage dropped below 3V3 (if that is your output voltage) then 3V3 will continue to be produced. When in UVLO mode, quiescent current is less than 2 uA.

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  • \$\begingroup\$ Will the current draw of the comparator not also cause a continued drain on the battery, or is it negligible? Also, if I have a comparator, the only reference voltage I have is the battery voltage, so wouldn't my reference change along with the voltage I'm trying to compare to? \$\endgroup\$
    – Sensors
    Jul 23, 2015 at 11:11
  • \$\begingroup\$ I'm not saying it's easy but you can get micropower references. It's all about managing the li-ion battery to leave enough headroom so that a small residual current draw allows you hours or days to sit around before recharging the battery. \$\endgroup\$
    – Andy aka
    Jul 23, 2015 at 11:31
  • \$\begingroup\$ linear.com/product/LTC1540 this might help \$\endgroup\$
    – Andy aka
    Jul 23, 2015 at 11:35

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