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P2 lithium battery — Parallax Forums

P2 lithium battery

pic18f2550pic18f2550 Posts: 392
in Propeller 2

Hello,
is it possible to power the P2 (3.3V) from a lithium battery?
The 1.8V still come via a regulator from the battery.

Does anyone have experience with this?

Comments

  • roglohrogloh Posts: 5,187
    edited 2021-12-07 23:38

    My own battery powered project uses a lithium battery to power the P2. I have 2 cells in series but I used two switching regulators to drop down to 3.3V and 1.8V. Lithium-Ion and LiPo cells can go as high as 4.2-4.35V or so when fully charged and it would not be good to try to run the P2 that high if you plan to use the battery voltage directly as the VCCIO voltages without a regulator. Although if you chose to use a LiFePO4 battery it would be a better match over the operating voltage range and you could potentially directly wire it to the P2's 3.3V supply. You can then keep the cell below 3.65V and the P2 would be happier.

  • pic18f2550pic18f2550 Posts: 392

    Ok,
    I'll have to use two cells.
    Switching regulators are out of the question because of the high interference on the voltage side and the interference radiation.
    A cascade of LDO controllers will have to provide a remedy.
    Thank you.

  • roglohrogloh Posts: 5,187
    edited 2021-12-08 00:19

    Unfortunately you will burn a lot of power with two cells and linear regulators. 8.4V dropped to 3.3V and 1.8V with LDOs wastes most of the energy as heat. If that wastage is not a concern then it is at least clean from a voltage supply point of view.

    You could consider a single Lithium cell and a 3.3V LDO, you'll just lose some regulation at the lower end of the battery voltage range when the regulator drops out. Might not be an issue depending on how low a voltage your application can run.

    The main reason my own application used two cells is that I needed to get 5V as well, which was easier to obtain from something varying from 6-8.4V than stepping up from 3-4.2V and then requiring even more current from the cells.

  • pic18f2550pic18f2550 Posts: 392
    edited 2021-12-08 10:33

    The battery should already hold something. :)
    The waste heat will end up being noticeable, in terms of size and weight.

    I just ask myself the question to what extent interference signals on the 1.8V affect the ADCs.
    Actually not because siese could be fed from the 3.3V. But this can only answer someone who is familiar with the innards of the P2. I can also supply the DAC pins via their own 3.3V power supply, which should further reduce the interference signals.

    1. regulator from battery (2 cells) to 5V (1,5A) with heat sink.

    2. regulator from 5V to 1,8V (800mA) P2 clk = 80 Mhz

    3. regulator from 5V to 3,3V (100mA) control circuits

    4. regulator from 5V to 3,3V (100mA) 8x ADCs

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