LDO power system in wearable

Question

I'm designing a wearable with a ESP32 and three drivers, everything works with 3,3 V and the drivers consumes 15 mA each one.

I'm powering it with a lithium battery of 400 mAh, (4.2 V max). So I thought to use an LDO the AP2112, but I have several questions about the LDO. For example, the ESP32 in sleep mode consumes only 50 mA more or less, but when its in booting or some transactions it consume 300 mA and when you are in "RF mode" (transmitting with BLE) it consumes 250 mA. I would like that the wearable operates minimum two hours without charging it.

So this LDO has an output current of 600 mA, and quiescent current of 55 μA. My question is if the LDO only consumes 55 μA and it is giving to me 600 mA "for free". But it doesn't make too much sense because I only use 55 μA for power a 500 mA (max) circuit. So it will be switched on like too much hours. With a 400 mAh battery.

And the second question is: if my ESP32 is consuming only 50 mA but the LDO gives to me 600 mA it could be some "overload" in circuit?

I read a lot of documentation but I don't know yet how it really works.

Answer 1

So this LDO has an output current of 600 mA, and quiescent current of 55 μA.

That means that the maximum current the regulator can provide is 600 mA. The quiescent current is the current drawn by the circuitry in the regulator even when there is no load.

My question is if the LDO only consumes 55 uA and it is giving to me 600 mA "for free".

No. If you have a 600 mA load then you have to provide the regulator with 600.055 mA.

But it doesn't make too much sense because i only use 55 uA for power a 500 mA (max) circuit.

Good. You are able to sense that there is a "free energy" scheme here and that is impossible!

So it will be switched on like too much hours. With a 400 mAh battery.

Calculate your average current. \$ Runtime = \frac {mAh}{mA} \$.

If my ESP32 is consuming only 50 mA but the LDO gives to me 600 mA it could be some "overload" in circuit?

The regulator will only provide whatever current your ESP32 draws. It doesn't "push" current that isn't required. Think: if you plug a 5 W LED lamp into your house supply that can provide 20 kW does the lamp use 20 kW or 5 W?