SNAS305J July 2005 – March 2016 ADC121S021
PRODUCTION DATA.
The ADC requires a single voltage supply within 2.7 V and 5.25 V.
The charging of any output load capacitance requires current from the power supply, VA. The current pulses required from the supply to charge the output capacitance causes voltage variations on the supply. If these variations are large enough, they could degrade SNR and SINAD performance of the ADC. Furthermore, discharging the output capacitance when the digital output goes from a logic high to a logic low dumps current into the die substrate, which is resistive. Load discharge currents causes ground bounce noise in the substrate that degrades noise performance if that current is large enough. The larger the output capacitance, the more current flows through the die substrate and the greater is the noise coupled into the analog channel, degrading noise performance.
To keep noise out of the power supply, keep the output load capacitance as small as practical. It is good practice to use a 100-Ω series resistor at the ADC output, located as close to the ADC output pin as practical. This limits the charge and discharge current of the output capacitance and improve noise performance.