LTC1863/LTC1867: How will I convert adc-code to voltage value?

Hi Andreas,

Assuming the ADC is set for bipolar operation, the output code will be in 2's complement notation. Figure 8 of the LTC1867 data sheet indicates what the output code will be for several different input voltages. For bipolar operation input voltages below 2.048 will be negative (The MSB will be 1). Input voltages above 2.048V will be positive (The MSB will be 0). The code you see will depend on where you bias the COM pin. Ideally COM should be biased at VREF/2. COM cannot be connected to ground for bipolar operation as this would limit your input range to 0V-2.048V.

Remember that the SDI word you give the ADC is for the next conversion, the SDO word you shift out as you shift in SDI is from the previous conversion. This doesn't matter if you are giving the ADC the same SDI configuration each time.

If you can provide an oscilloscope photo showing CONV, SCK and SDO, I can decode it for you.

Hi Andreas,

Assuming the ADC is set for bipolar operation, the output code will be in 2's complement notation. Figure 8 of the LTC1867 data sheet indicates what the output code will be for several different input voltages. For bipolar operation input voltages below 2.048 will be negative (The MSB will be 1). Input voltages above 2.048V will be positive (The MSB will be 0). The code you see will depend on where you bias the COM pin. Ideally COM should be biased at VREF/2. COM cannot be connected to ground for bipolar operation as this would limit your input range to 0V-2.048V.

Remember that the SDI word you give the ADC is for the next conversion, the SDO word you shift out as you shift in SDI is from the previous conversion. This doesn't matter if you are giving the ADC the same SDI configuration each time.

If you can provide an oscilloscope photo showing CONV, SCK and SDO, I can decode it for you.

Hi, 

Thank you for your response!

My mistake was the SPI clock, I have used different clock speed from master and slave.

Thanks, Andreas