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ADC input range on 28377D 16-bit differential mode

In Technical Reference Manual, it says that when -VERFHI < (ADCINyP-ADCINyN) < VERFHI, the result would be 65535 * ((ADCINyP-ADCINyN+VREFHI)/(2 * VREFHI)).

But what is the range of ADCINyP or ADCINyN? I can't find the differential input range of ADC.

Can I apply a negtive voltage on ADCINyP?

  • Hi,

    Check this thread out: e2e.ti.com/.../1174972

    Regards,
    Gautam
  • Thanks for your reply.

    I have read the post.

    The common mode voltage means (INyP+INyN)/2, if I have a +-15V signal, I need to convert it to +-100mV, then add a VREFHI/2 bias, connect it to INyP, and connect the VREFHI/2 bias to INyN. When using 3V as referece, the INyP signal range would be 1.4V-1.6V, right?

    But in this way, I can only get about 32768 +- 2148 data range, right?

    Now I connect INyP to 0-3V siginal, and INyN connected to AGND, I can also got a right value, from 32768 to 65535. What will happen to the processor when it works under this situation in a long time ? What does the recommend common mode voltage mean?

    The only way to get full range is using a differential amp?

  • ccen3020,

    If you have a +/-15 V signal, you need to reduce the amplitude to 0 to VREFHI and the offset to be VREFHI/2. The positive ADC input gets a varying signal in the range of 0 to VREFHI. The negative input also gets a varying signal in the range of 0 to VREFHI, but it is the complement of the positive input about VREFHI/2. The sum of the positive and negative input is always VREFHI (as the positive input increases, the negative input decreases and vice versa). If you put a static voltage into either the positive or negative input (e.g. connect one to ground) the ADC will not work (the range is not reduced).
  • For I didn't noticed the differental input requirment, I designed the circult in a wrong way, and the board has been made.

    My circult likes above picture. The op is used for reducing and adding offset, then connect to DSP throught the RC network.

    I had tried to connect INyN to AGND and INyP to a 0-3V singal yesterday, It seems that the ADC could work well on 16bit mode(the accuracy not been tested yet).

    So what does it mean that the ADC will not work while connecting one input to a static voltage?

  • If the DS common mode voltage requirements are not met, the DS spec's are not guaranteed.  From a practical perspective, the performance will certainly be worse than DS spec's, but we haven't done any characterization to know how bad the performance will be.