The ADC121C021 is a low-power, monolithic, 12-bit, analogto-digital converter(ADC) that operates from a +2.7 to 5.5V supply. The converter is based on a successive approximation register architecture with an internal track-and-hold circuit that can handle input frequencies up to 11MHz. The ADC121C021 operates from a single supply which also serves as the reference. The device features an I2C-compatible serial interface that operates in all three speed modes, including high speed mode (3.4MHz). The ADC's Alert feature provides an interrupt that is activated when the analog input violates a programmable upper or lower limit value. The device features an automatic conversion mode, which frees up the controller and I2C interface. In this mode, the ADC continuously monitors the analog input for an "out-of-range" condition and provides an interrupt if the measured voltage goes out-of-range. The ADC121C021 comes in a small TSOT-6 package with an alert output. The ADC121C027 comes in a small TSOT-6 package with an address selection input. The ADC121C027 provides three pin-selectable addresses. Pin-compatible alternatives are available with additional address options. Normal power consumption using a +3V or +5V supply is 0.26mW or 0.78mW, respectively. The automatic powerdown feature reduces the power consumption to less than 1W while not converting. Operation over the industrial temperature range of -40C to +105C is guaranteed. Their low power consumption and small packages make this family of ADCs an excellent choice for use in battery operated equipment. The ADC121C021 and ADC121C027 are part of a family of pin-compatible ADCs that also provide 8 and 10 bit resolution. For 8-bit ADCs see the ADC081C021 and ADC081C027. For 10-bit ADCs see the ADC101C021 and ADC101C027.