Hi,
What is the board input voltage?. The 4 AAA batteries supply 6V, but the backup is 3.2V.
Is the 3.2V intended to support the memory?
So 6V is the nominal input to the board?
Thanks
If you look at the
datasheet of a modern memory IC you'll see that the supply voltage level needed for data retention in standby mode is much lower than the nominal operating voltage. The current draw in standby is also tens of thousands of times lower than operating level.
The HP 50g has four batteries, i.e., 6 V and can be USB powered (5 V). The HP 49G+ has three batteries, i.e., 4.5 V and I guess the underlying technology is the same. So, without having on hand any schematic diagram, there are chances that the internal electronics works at 3.3 V and an efficient voltage regulator is used to convert these input voltages (6 V, 5 V or 4.5 V) to the 3.3 V operating voltage of the ARM microcontroller and rest of the electronics.
Currently there are in the market amazingly efficient buck-boost voltage regulators for this task.