Datasheet

ADC081S051
SNAS309E –APRIL 2005–REVISED MARCH 2013 www.ti.com
POWER SUPPLY NOISE CONSIDERATIONS
The charging of any output load capacitance requires current from the power supply, V
A
. The current pulses
required from the supply to charge the output capacitance will cause 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 will dump current
into the die substrate, which is resistive. Load discharge currents will cause "ground bounce" noise in the
substrate that will degrade 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 will
limit the charge and discharge current of the output capacitance and maintain noise performance .
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