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MSP430F5529: Powering issues

Part Number: MSP430F5529
Other Parts Discussed in Thread: MSP-EXP430F5529LP,

Hello all, I'm having some strange powering issues with MSP-EXP430F5529LP board.

What I was trying to do is to have one external 3.3V power source that alimentates MSP430F5529, from 3.3V and GND pins; but at the same time I wanted the UART 1 to be available.

So I removed the alimentation jumpers in the isolation block (3.3V and 5V). The weird thing is that in this condition, without the external power source, but just the USB cable, I still notice some voltage on 5V and 3.3V pins. I tried removing jumpers one by one and I realized that was the RX jumper that was alimentating those pins. Without it the voltage was 0, as expected.

Someone could explain me why and how do I fix it?

  • Hi Lorenzo,

      As shown in the schematic, you only need to disconnect the 5V and 3.3V terminals. When you connect RX jumper, the RX has a signal, so that the power supply on the MCU voltage is not 0V but less than 3.3V.

    Best Regards,

    Johnson

  • Hello,
    Thank you for the answer! But why with the RX jumper connected and both 3.3V and 5V jumpers disconnected I still can read a signal on MCU pins? That's what I don't understand

  • Hi Lorenzo,

    The MSP430 has a clamping diode on each pin during the design process. as shown in the following figure.

    The RXD jumper connect to the TXD of the FET-DEBUG. This pin is pulled high by the FET in the idle state. Therefore, It's similar to provide the 3.3V power  to the I/O pin, the VDD has a voltage through D1, so the MCU work. but this situation is not allowed, which may cause problems in the internal FRAM of the MCU, and the upper limit current of the clamp diode is only 2MA.

    Best Regards,

    Johnson

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