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These converters are low-power, monolithic, 12-bit, analog-to-digital converters (ADCs) that operates from a +2.7 to 5.5V supply. The converter is based upon a successive approximation register architecture with an internal track-and-hold circuit that can handle input frequencies up to 11MHz. These converters operate 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 ADC121C021'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 two packages: a small 6-pin SOT package with an alert output, and an 8-pin VSSOP package with an alert output and two address selection inputs. The   ADC121C021Q is available in a 6-pin SOT package. The ADC121C027 comes in a small 6-pin SOT package with an address selection input. The ADC121C027 provides three pin-selectable addresses while the 8-pin VSSOP version of the ADC121C021 provides nine pin-selectable addresses. Pin-compatible alternatives to the 6-pin SOT options are available with additional address options.

Normal power consumption using a +3V or +5V supply is 0.26mW or 0.78mW, respectively. The automatic power-down feature reduces the power consumption to less than 1µW while not converting. Operation over the industrial temperature range of −40°C to +105°C is ensured. 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.