SNAS483F February 2010 – August 2015 ADC128D818
PRODUCTION DATA.
The ADC128D818 operates with a supply voltage, V+, that has a range between 3 V to 5.5 V. Take care to bypass this pin with a parallel combination of 1-µF (electrolytic or tantalum) capacitor and 0.1-µF (ceramic) bypass capacitor.
The reference voltage (VREF) sets the analog input range. The ADC128D818 has two options for setting VREF. The first option is to use the internal VREF, which is equal to 2.56 V. The second option is to source VREF externally through pin 1 of ADC128D818. In this case, the external VREF will operate in the range of 1.25 V to V+. The default VREF selection is the internal VREF. If the external VREF is preferred, use the Advanced Configuration Register — Address 0Bh to change this setting.
VREF source must have a low output impedance and needs to be bypassed with a minimum capacitor value of 0.1 µF. A larger capacitor value of 1 µF placed in parallel with the 0.1 µF is preferred. VREF of the ADC128D818, like all ADC converters, does not reject noise or voltage variations. Keep this in mind if VREF is derived from the power supply. Any noise and/or ripple from the supply that is not rejected by the external reference circuitry will appear in the digital results. The use of a reference source is recommended. The LM4040 (SLOS746) and LM4050 (SNOS455) shunt reference families as well as the LM4120 (SNVS049) and LM4140 (SNVS053) series reference families are excellent choices for a reference source.