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MSP430F67641A: Unexpected behaviour incase of changes in AC voltage status

Part Number: MSP430F67641A
Other Parts Discussed in Thread: MSP-FET

Dear Team,

We have designed a 3 phase Power monitoring system for AC lines, based on  MSP430F67641A and we have some real time abnormalities.

  • The device works fine in normal conditions, but when the AC lines are powered up the active debug session via FET430 hangs and i have to restart.
  • Once the AC lines are active the controller runs with no issues, but when i try to induce a flicker in the AC by just switching OFF and back ON, i get a complete restart of the module.

Is this expected ?. Could you please help me here.

My expectation was that since we handle AC lines directly, and this is a specialised controller dedicated for this application, i had a better expectation that the controller can withstand the AC noise induced if any. 

The module is the exact replica of the reference design from the evaluation module (

Thanks in advance,


  • Hello,

    I suspect that the AC lines are powering the MSP430 rather than the MSP-FET or bench power supply. If not, perhaps there's a power supply conflict. For example, you may be powering the board with the MSP-FET but when AC lines are powered on, an onboard power supply also starts providing voltage to the device. If the device loses power, I would expect the debug session to hang. You can find more details about the VCC jumper settings in the EVM user guide.

  • Hi, Thanks for this hint.

    I tried different combinations to identify the reset source, and the reset of the controller is triggered from the MSP-FET "RST" pin to the controller.I juts tried removing the FET alone from my setup and the overall reset issue is gone. Not sure why this happens from FET to reset the controller where there is a fluctuation, but when i trigger a fresh debug session with the AC mains ON hen it works, but the FET does not like any voltage changes from outside.

    And just for info, i am powering up the module from an external voltage source. And i have a common mode choke filter on the DC lines (like a PI filter) before the voltage regulator. I am not that good on the circuit side to judge here, maybe the ground lines are synced up with the ground line via a common mode inductor. Could this cause an issue basically ?.   

  • Nice work! There may be noise or spikes getting introduced to the MSP-FET causing it to send a reset to the target. In most of these designs, the ground is connected to Neutral. Some customers reverse those connections and then Line is connected to ground - this would be dangerous because the ground is connected to the MSP-FET and could damage your PC or you personally. Just be very cautious when connecting the MSP-FET to the board with AC mains enabled without using isolation.

    For your MSP-FET connections, make sure you are connecting Pin 4 (VCC_TARGET) to VCC rather than Pin 2 (VCC_TOOL). VCC_TARGET should be used with external power supplies and is used to sense the supply voltage in order to set the logic levels of the JTAG signals.

    Adding a choke should help reduce noise. For the AC mains, there may be inrush current that is causing voltage spikes on certain signals on your board. Discrete ESD components are helpful to attenuate spikes, and some are included in the EVM design. You can also add low-resistance inline resistors to limit current on traces as well.

  • Great, Thanks a lot for your support and suggestions here. That really helped to solve my problem

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