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The microcontroller and several sensors of my circuit draw 10µA in sleep mode. I am using a 100mAh lithium polymer battery. Is this quiescent current acceptable? Should I install a physical switch to shut down the device completely?

Should I install a p channel MOSFET on the voltage rail of my sensors to reduce the quiescent current down to 3µA?

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    \$\begingroup\$ Please pay attention to case for SI units: ampere is upper case A, lower case a is year (from latin annum); hour is lower case h, upper case H is Henry, the unit for inductance. \$\endgroup\$
    – starblue
    Feb 5, 2011 at 9:31
  • \$\begingroup\$ How long does it need to last in standby mode? \$\endgroup\$ Feb 5, 2011 at 11:28

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This is actually a rather straightforward calculation, but you might need more data than provided.

Wikipedia says LiPo has a 5%/month self-discharge rate, so even with zero current draw you have 20 months standby. 5%/month * 100mAh is about 7 uA current draw.

So we'll say the combined discharge at 10 uA is 17uA. 100mAh / 17uA = 5900 hours standby time. This is about eight months. Is this sufficient for you? If you knock your standby down to 3uA you can get about a year standby.

Notice that all these calculations are assuming a lot of things. You won't always be in standby mode if your circuit does something useful, so you should add in active current * duty cycle. And of course battery chemistry is complicated, so these are just ballpark figures until you actually build and measure the circuit.

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  • \$\begingroup\$ 5% per month doesn't mean that it's completely drained after 20 months. It's exponential: the second month it's 5% of the remaining 95%. Continuing like that after 20 months there should be 36% of the energy left. \$\endgroup\$
    – stevenvh
    Jul 31, 2011 at 14:17

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