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ADS1248 calculation

Embedded World
Prodigy 170 points

Other Parts Discussed in Thread: ADS1248

How to convert analog value from digital value

1. I am using internal ref = 2.048V , PGA = 1V & input voltage = +-2.048V.

Since it is 24 bit adc with msb for sign, so I get conversion  factor= 2^23 - 1= 8388607.

So when I read +ve input voltage with digital data = 0x002222 = 8738d,

then analog value = 8738 / 8388607 = 1mV around

Similarly for -ve value i.e = 0x802222

then analog value = 0x802222 / 2^23

Is it right way to convert between values

  • 0
    TI__Guru** 113765 points

    Hi Embedded,

    Each count (LSB) of the ADC is related to the value of the reference is some way.  For the ADS1248, this equates to 2*Vref/(PGA*(2^24-1)).  This is the full-scale range of the converter (2*Vref/PGA) divided by the total number of counts available (2^24-1).  This can be simplifed to Vref/(2^23-1) when using PGA equal to 1.  The internal reference of the ADS1248 is 2.048V, so one count is equal to 2.048/(2^23-1) volts.

    To get the measured voltage you take the value of one count (above equation) and multiple the value by the total number of counts given by the converter.  The result is the input voltage applied to the ADC.

    Best regards,

    Bob B