How to regulate a 3.6 V battery to two power rails (3.3 V and 1.8 V)

batterieslow-powerpowervoltage dividervoltage-regulator

I have a 3.6 V battery from which I need two voltage rails, one that is 3.3 V and one that is 1.8 V. How should I design this circuit such that it is the most power efficient?

Here is what I was thinking:

  • Using one voltage regulator to regulate the 3.6 V down to 3.3 V, and using voltage division after the 3.3 V to create a 1.8 V
  • Using two voltage regulators to regulate the 3.6 V down to 3.3 V and 1.8 V

Are either of these good options? What else might you suggest?

Follow-up question about using two regulators: Should I put them in series or parallel?

i.e.

Series: Regulate 3.6 V down to 3.3 V, and then regulate this 3.3 V down to 1.8 V.

Parallel: Regulate 3.6 V down to 3.3 V, and separately regulate 3.6 V down to 1.8 V.

schematic

simulate this circuit – Schematic created using CircuitLab

Best Answer

My load current for the 3.3 V rail is 546.2 mA. My load current for the 1.8 V rail is 1.154 mA.

Your 1.8V rail is basically just a reference voltage. A voltage divider from a regulated source would work just fine. A 1.8V 1.154 mA load is like a 1500kΩ load, keep that in mind when you make your voltage divider. Efficiency isn't really an issue here. Even at 50% efficiency, that's 4mW.

As for the 3.3V rail, with a 3.6V battery, likely a lithium battery, you want a buck-boost switching regulator, as the voltage range of the battery will be above AND below 3.3V. You want it to regulate down, and then regulate up. Look for one based on your battery chemistry, as there are some that have built in battery protection, to prevent it from draining too low.

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