MCU power supply design

I am working with a micro controller based board design. We need to power this board from another micro controller based board that has regulated 3.3V power output connector. These two boards will be connected by a one foot cable for power and UART. The micro in the board we are designing needs 3.3V for its peripherals and SDRAM and

1.2V for the core.

Is it OK to give regulated 3.3V from another board directly (using adequate bypass capacitors) for this micro's peripheral and SDRAM and through an LDO or switching regulator outputting 1.2V to the core? The

3.3V supply will have source approx 500ma current which is sufficient for my board.

- bhav

Reply to
Bhavani
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Does the source have enough current ability? How long are the wires?

Reply to
MooseFET

I would not be concerned about how much current the other board can source, but more, how much current YOUR board needs. This will determine the voltage drop in the 1 foot cable.

Personally, I would want to pass a higher voltage down the cable (if available) as this will then allow for a voltage drop down the cable. You can then locally regulate the 'cable' supply to provide 3v3 for your processor.

If you are using a switched power supply on your local board, this will take peaks of current greater than the average current demanded by your circuit, and this will manifest itself as ripple on the input to your board due to the impedance of the 1 foot cable. switched solution therefore not a good idea.

Also, if the 3v3 coming out of the other board is on the low side, the cable impedance might ensure your 3v3 at the receive end is well below tolerance.

If you can pipe a higher voltage down the cable, this is the best solution. Capacitors (as you mention) will not replace a voltage that was never there.

Failing that, put a boost converter on the front end of your board to boost any voltage drop lost in the cable.

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Bill
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Electronworks.co.uk

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Tanks a lot Bill. Our board draws peak current of 0.3 to 0.4A and the only voltage available from the other board is regulated 3.3V. In our board the required voltages are 1.2V for the core and 3.3V for the microcontroler's peripherals, SDRAM and audio DAC.

-bhav .

Reply to
Bhavani

Primary rule: always have regulators, overvoltage and reverse polarity protection on board. There are many scenarios in which things can go wrong (too much voltage drop, wrong connection, etc).

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Reply to
Nico Coesel

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