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CCS/MSP430G2433: AIN3 and AIN4 Pins EMC Problem

Part Number: MSP430G2433

Tool/software: Code Composer Studio


I am testing a circuit for EMC between 80MHz-230MHz frequencies. I face a problem on analog inputs A3 and A4. Under test, I read high analog values. For understanding the reason easily, all analog inputs were seperated from circuits connected. When apply frequencies, I am seeing abnormal voltages on A3 and A4 again. However, other analog inputs stay in normal state. That means only A3 and A4 have different behaviours from others.

In MSP430x2xx Family User's Guide, Figure 22-1. ADC10 Block Diagram shows that A3 and A4 are connected to referance voltage part. I guess, the problem is starting from here. I configured some registers as below. However, I cannot resolve the problem.
ADC10CTL0: SREFx is '000' (VR+ = VCC and VR- = VSS)
ADC10CTL0: REFOUT is 0 (Reference output off)
AC10CTL0: REFON is 0 (Reference off)

Do you have any suggestions ?

Thank you.

  • Hello,

    I'd like to suggest you do below tests.

    1. Get a series of samples in A3/A4. Then performing a FFT to see the spectrum  to determine if it's interfered by 80MHz-230MHz source.

    2. Capture the signal in A3/A4 pin using oscilloscope to see if it's interfered by 80MHz-230MHz source.

    3. Review your PCB layout and routing. If any difference between A3/A4 and other analog input pin.

    4. Apply low-pass filter at A3/A4 and measure again.

  • Thank you for your reply,

    Firstly, I cut the analog inputs tracks on board. That means I leaved pins as bare. I measured all analog input voltages under test with a voltmeter. Measured values are same with read analog values in software. Actually, I guess I don't need a filter circuit and I need to seperate these pins from reference part.

  • Could you get a series of samples in A3/A4, and then performing a FFT to see the spectrum  to determine if it's interfered by 80MHz-230MHz source?