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Powering MSP430F5529 LaunchPad with 2.8V instead of 3.3V - any obstacles?

tml
Expert 1140 points
Other Parts Discussed in Thread: MSP-EXP430F5529LP, MSP430F5529

Hi,

In my hobby weather station I use an MSP-EXP430F5529LP powered from the boosterpack connectors.

Now I'd like to start using an MT9D111 camera for capturing still photos but the voltage on the camera's interface cannot exceed 3.1V, ideally 2.8V. Instead of having a voltage translator for dozen of communication lines I'd rather lower the MCU's Vcc from 3.3V to 2.8V.

The question is whether I should expect any issues with LaunchPad components and MCU itself when lowered the voltage to 2.8V?
The datasheet is clear that the MSP430F5529 can be supplied with voltage of 1.8-3.6V so the only problem might be whether there are any 3.3V-dependent components on the LaunchPad.

Best Regards,
tml

  • 0
    Guru 12956 points

    The eZFET portion will run at 3.3V regardless since it gets its power from the onboard DC-DC converter.  So you could program it (without connecting the 2.8V power source or the camera), then disconnect most of the headers on the eZFET (e.g. 3.3V, UART RXD/TXD, RESET and TEST) and hook up your 2.8V source + camera to the bottom portion of the launchpad.

    If you need UART backchannel support, you might be able to get away with keeping the UART TXD pin hooked up so the eZFET will be able to receive signals from the MSP430.

  • 0 in reply to Eric Brundick
    Expert 1140 points

    Thanks!

    Is that possible to program the MCU powered with 2.8V with the eZFET powered with 3.3V? I mean I can try doing that (with not taking off the 3V3 jumper) but would not like to bake the MCU's internals ;-)

    Regards
    tml

  • 0 in reply to tml
    Guru 227245 points

    There is a way to at least use the application UART:
    Pull all jumpers between MCP and FET

    For RX and TX, connect MSP and FET with a diode, cathode (ring) directed to the signal source, and a pull-up from anode to the destination’s VCC.
    This can make up for at least 30% voltage difference.

    However, this only works for uni-directional signals. And SBW, as used for the debugging and uploading, is bi-directional.
    Well, another option is to live with some wasted energy and put a 4k7 series resistor in place of the jumpers (all but VCC, which must remain removed). It should work too, as the MSP is capable of taking up to 2mA input current due to overvoltage. And the series resistor will have a voltage drop of 4,7V/mA, limiting the current to 0.2mA/(Vin-Vcc). A rather dirty solution but better than nothing.
    Still outputs from MSP to FET need to reach 0.7*Vcc(FET) to be sure to be recognized as high. So the voltage difference mus tnot be too high. You can't run an 1.8V MSP from a 3.6V FET this way.

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