AD7291

The AD7291 is a 12-bit, high speed, low power, 8-channel,successive approximation ADC with an internal temperature sensor. The part operates from a single 3.3V power supply and features an I2C®-compatible interface. The track-and-hold amplifier which can handle input frequencies of up to 70MHz,and a multiplexer allows samples from eight channels.For AC applications, removing high frequency components from the analog input signal is recommended by using an RC low-pass filter on the relevant analog input pin. In applications where harmonic distortion and signal-to-noise ratios are critical, the analog input should be driven from a low impedance source. Large source impedances significantly affect the ac performance of the ADC.

Features of the AD7291 are:(1)8 single-ended inputs; (2)channel sequencer functionality; (3)analog input Range 0 to 2.5V; (4)12-bit temperature-to-digital converter; (5)internal 2.5V reference.The AD7291 typically remains in a partial power-down state while not converting. When supplies are first applied, the parts power up in a power-down state. Power-up is initiated prior to a conversion, and the device returns to shutdown when the conversion is complete. Conversions can be initiated using the autocycle mode or command mode where the wake-up and a conversion occur during a write address function.

The absolute maximum ratings of the AD7291 can be summarized as:(1)VDD to AGND, DGND:-0.3V to +5V;(2)storage temperature range:-65 to +150;(3)soldering temperature:260;(4)junction temperature:150;(5)analog input voltage to AGND:-0.3 V to 3V;(6)input current to any pin except supplies:±10 mA.Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.The AD7298 is a 12-bit successive approximation ADC based around a capacitive DAC. Figure 4 and Figure 5 show simplified schematics of the ADC. The ADC is comprised of control logic, SAR, and a capacitive DAC that are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition.