Return to Answer

I am powering a PIR sensor which has minimum 3.4V of VCC and 70µA supply current with parallel Li-ion batteries

You can get a buck (not boost) regulator than consumes less than 20 μA and will run from series cells and, although your load current is 70 μA at 3.6 volts, when the two series cells are producing a voltage in the range 8.4 volts down to 5.4 volts, the current drawn from the cells will be less than 70 μA due to the buck converter's power efficiency. It's not like a linear regulator.

If the two series cells are at nominally 3.7 volts each, the voltage into the buck will be 7.4 volts and, the load current drawn by the sensor won't be 70 μA from the cells but more like 39 μA. Add to this the nominal current taken by the buck and that means less than 60 μA taken from your battery arrangement.

If you used something like the LTC3632, it has a nominal quiescent current of only 12 μA. Two series cells (instead of two parallel cells) allows the cells to discharge to their lower recommended limit thus giving you more life from your batteries and still enough voltage to regulate down to 3.6 volts: -

And, there are bucks with even lower quiescent current when run it burst mode.

I am powering a PIR sensor which has minimum 3.4V of VCC and 70µA supply current with parallel Li-ion batteries

You can get a buck (not boost) regulator than consumes less than 20 μA and will run from series cells and, although your load current is 70 μA at 3.6 volts, when the two series cells are producing a voltage in the range 8.4 volts down to 5.4 volts, the current drawn from the cells will be less than 70 μA due to the buck converter's power efficiency. It's not like a linear regulator.

If the two series cells are at nominally 3.7 volts each, the voltage into the buck will be 7.4 volts and, the load current drawn by the sensor won't be 70 μA from the cells but more like 39 μA. Add to this the nominal current taken by the buck and that means less than 60 μA taken from your battery arrangement.

If you used something like the LTC3632, it has a nominal quiescent current of only 12 μA. Two series cells (instead of two parallel cells) allows the cells to discharge to their lower recommended limit thus giving you more life from your batteries and still enough voltage to regulate down to 3.6 volts: -

And, there are bucks with even lower quiescent current when run in burst mode such as the LT8618C.

I am powering a PIR sensor which has minimum 3.4V of VCC and 70µA supply current with parallel Li-ion batteries

You can get a buck (not boost) regulator than consumes less than 20 μA and will run from series cells and, although your load current is 70 μA at 3.6 volts, when the two series cells are producing a voltage in the range 8.4 volts down to 5.4 volts, the current drawn from the cells will be less than 70 μA due to the buck converter's power efficiency. It's not like a linear regulator.

If the two series cells are at nominally 3.7 volts each, the voltage into the buck will be 7.4 volts and, the load current drawn by the sensor won't be 70 μA from the cells but more like 39 μA. Add to this the nominal current taken by the buck and that means less than 60 μA taken from your battery arrangement.

That's an improvement for sure and, if you used something like the LTC3632, it has a nominal quiescent current of only 12 μA. Two series cells (instead of two parallel cells) allows the cells to discharge to their lower recommended limit thus giving you more life from your batteries and still enough voltage to regulate down to 3.6 volts: -

I am powering a PIR sensor which has minimum 3.4V of VCC and 70µA supply current with parallel Li-ion batteries

You can get a buck (not boost) regulator than consumes less than 20 μA and will run from series cells and, although your load current is 70 μA at 3.6 volts, when the two series cells are producing a voltage in the range 8.4 volts down to 5.4 volts, the current drawn from the cells will be less than 70 μA due to the buck converter's power efficiency. It's not like a linear regulator.

If the two series cells are at nominally 3.7 volts each, the voltage into the buck will be 7.4 volts and, the load current drawn by the sensor won't be 70 μA from the cells but more like 39 μA. Add to this the nominal current taken by the buck and that means less than 60 μA taken from your battery arrangement.

If you used something like the LTC3632, it has a nominal quiescent current of only 12 μA. Two series cells (instead of two parallel cells) allows the cells to discharge to their lower recommended limit thus giving you more life from your batteries and still enough voltage to regulate down to 3.6 volts: -

And, there are bucks with even lower quiescent current when run it burst mode.

You can get a buck regulator than consumes less than 20 μA and will run from series cells and, although your load current is 70 μA at 3.6 volts, when the two series cells are producing a voltage in the range 8.4 volts down to 5.4 volts, the current drawn from the cells will be less than 70 μA due to the buck converter's power efficiency. It's not like a linear regulator.

If the two series cells are at nominally 3.7 volts each, the voltage into the buck will be 7.4 volts and, the load current drawn by the sensor won't be 70 μA from the cells but more like 39 μA. Add to this the nominal current taken by the buck and that means less than 60 μA taken from your battery arrangement.

That's an improvement for sure and, if you used something like the LTC3632, it has a nominal quiescent current of only 12 μA. Two series cells (instead of two parallel cells) allows the cells to discharge to their lower recommended limit thus giving you more life from your batteries.

I am powering a PIR sensor which has minimum 3.4V of VCC and 70µA supply current with parallel Li-ion batteries

You can get a buck (not boost) regulator than consumes less than 20 μA and will run from series cells and, although your load current is 70 μA at 3.6 volts, when the two series cells are producing a voltage in the range 8.4 volts down to 5.4 volts, the current drawn from the cells will be less than 70 μA due to the buck converter's power efficiency. It's not like a linear regulator.

If the two series cells are at nominally 3.7 volts each, the voltage into the buck will be 7.4 volts and, the load current drawn by the sensor won't be 70 μA from the cells but more like 39 μA. Add to this the nominal current taken by the buck and that means less than 60 μA taken from your battery arrangement.

That's an improvement for sure and, if you used something like the LTC3632, it has a nominal quiescent current of only 12 μA. Two series cells (instead of two parallel cells) allows the cells to discharge to their lower recommended limit thus giving you more life from your batteries and still enough voltage to regulate down to 3.6 volts: -