NRF51822 with AA Batteries

[Nate]

I am working on a school project using the NRF51822 with SoftDevice 130 on a custom board and I aim to create an HID gamepad. I am working on my power supply circuit and my device will be powered by two AA batteries in series. When the batteries are new they have a voltage of +3.0V and for ease of design let's say that once they drop below +1.8V (the minimum for the internal LDO) that they are "dead".

Is it feasible to connect the batteries directly to the AVDD, VDD and GND pins and use the internal LDO? Would it be better to use an external regulator and if so, which do you recommend?

[Dave_couling]

Its not necessary using an external LDO if the following conditions are met:

1. You have reverse polarity protection - highly necessary for a battery as often accidentally installed backwards as a AA or AAA
2. Assure under no circumstances the maximum input voltage is exceeded +3.6V
3. Add capacitance so can filter the power, and handle spikes went installing the Battery
4. A TVS is recommended to protect the nRF51 from voltage spikes from installing the battery.

[Nate]

I don't think it is possible to exceed 3.6V with AA batteries, but after having looked at some specs on rechargable batteries it would seem that I may want an external boost regulator after all because rechargable AA batteries are only 1.2V at full charge. I hadn't even thought of reverse polarity protection, so I will research some circuits for that. It would appear that directly using the LDO may be more suited for other applications where reversing the power source poles isn't a factor. I appreciate the input.