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ADC128D818: Limit Register and Interrupt Relation

Arin Cengiz
Prodigy 120 points
Part Number: ADC128D818

Hello,

In my design: 

- I am using external Vref (approximately 5V) and I coded external Vref condition in Advanced Config. Register outside of the while loop.

- Already coded interrupt mask register such that only IN1 can cause Interrupt issue.

- Again wrote Limit Register ( for high limit = 0xFF and low limit = 0x00 ) at outside of the while loop.

- Also wrote 0x03 inside of the Configuration Register (in order to activate Interrupt pin)

With these information:

- Even if there is 0V or 1V input on the IN1 pin, interrupt occurs. How does this comparison mechanism work and why do I observe this fault ?

Best Regards,

Arın

  • 0
    TI__Guru* 97905 points

    Arin,

    Normally, the interrupt would trigger when the voltage reading is greater than the voltage high limit or when the voltage is lower than the voltage low limit.

    The limit setting should be:

    Voltage limit = (ADC code)(Vref)/2^8

    Now, if you've set the high limit to FFh and the low limit to 00h, then the interrupt shouldn't trigger. I would first verify that the registers are correct and are correctly written. Read back the registers just to see that your write was correctly received by the device. I would also verify the input voltage by measuring it back with a multimeter.

    Are you using the device with a single-ended or pseudo-differential input? Are the limits on all inputs being flagged?


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 120 points

    Joseph,

    I was using the ADC device in single-ended mode. As you said, I controlled my limit registers value and corrected it. But I have still problem:

    - I am trying to measure sinusoidal voltage (1V peak, 2.5V DC offset, 10 kHz), and I want to see that interrupt occurs at INT pin when sinusoidal voltage is higher than 3V. (I used appropriate high and low limit registers)

    However, even if 10 kHz sinusoidal voltage passes from 3V, interrupt does not exist. What is the reason of that ? Does the frequency of the sinusoidal voltage (10 kHz) cause this issue, because when I used DC voltage value such as 3.2V, I can see the interrupt.

    Best regards,

    Arın

  • 0 in reply to Arin Cengiz
    TI__Guru* 97905 points

    Arin,


    The ADC128D818 has a data rate of about 80 samples per second at it's fastest. It will not be able to measure a 10kHz input signal. This device is a delta-sigma type ADC, which means that the input is oversampled. The input voltage is sampled many times to make a single output conversion data. This device does not use a sample-and-hold.

    In the ADS128D818, the data period is 12.2ms. During that entire period the input voltage is repeatedly sampled and basically averaged. Because of this, the ADC will have a frequency response that looks like a low pass filter, I would guess that the bandwidth is about 10Hz.

    Out of curiosity, what was the problem with the limit register values? I wasn't sure what you meant when you said you controlled and corrected it.


    Joseph Wu