The AD79841 is an 18-bit， successive approximation， analog-todigital converter （ADC） that operates from a single power supply， VDD. It contains a low power， high speed， 18-bit sampling ADC and a versatile serial interface port. On the CNV rising edge， the AD7984 samples the voltage difference between the IN+ and IN? pins. The voltages on these pins usually swing in opposite phases between 0 V and VREF. The reference voltage， REF， is applied externally and can be set independent of the supply voltage， VDD. The SPI-compatible serial interface also features the ability， using the SDI input， to daisy-chain several ADCs on a single 3-wire bus and provides an optional busy indicator. It is compatible with 1.8 V， 2.5 V， 3 V， and 5 V logic， using the separate VIO supply. The AD7984 is available in a 10-lead MSOP or a 10-lead LFCSP with operation specified from ?40°C to +85°C.