SBAU171D May 2010 – January 2016 ADS1198 , ADS1298
The MVDD input option allows the measurement of the supply voltage VS = (AVDD + AVSS)/2 for channels 1, 2, 5, 6, 7, and 8; however, the supply voltage for channel 3 will be DVDD/2. As an example, in bipolar supply mode, AVDD = 3.0V and AVSS = –2.5V. Therefore, with the PGA gain = 1, the output voltage measured by the ADC will be approximately 0.25V.
The RLD measurement takes the voltage at the RLDIN pin and measures it on the PGA with respect to (AVDD + AVSS)/2. This feature is beneficial if the user would like to optimize the gain of the RLD loop.
The voltage used to derive the right leg drive for both the positive and negative electrodes may also be measured with respect to (AVDD + AVSS)/2.