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Electronic Design

Delta-Sigma ADCs Interface Easily To Sensors

The LTC2480 delta-sigma analog-to-digital converters (ADCs) from Linear Technology feature a front-end design that can be driven directly from bridges, resistance-temperature detectors (RTDs), thermocouples, and other high-impedance sensors. This eliminates the drawbacks of on-chip buffering.

The company's Easy Drive technology yields zero average differential input current, simplifying the design of front-end signal conditioning circuits. Traditional delta-sigma ADCs employ switched-capacitor network input stages that switch between input, reference, and ground at rates that vary with the input signal level. In the LTC2480 series, though, charge/discharge current pulses are balanced.

When summed over the entire conversion cycle, the total differential input current is zero, independent of the differential input voltage, common-mode input voltage, reference voltage, or output code. This lets circuit designers place external RC networks with large time constants directly in front of the ADC without degrading its dc accuracy.

The LTC2480 provides 16-bit resolution with 2-ppm INL, 1-ppm offset, and 15-ppm full-scale errors. It features an internal temperature sensor and programmable gain up to 256, suiting it for temperature compensation of low-level sensors. The LTC2482 comes without the internal temperature sensor or programmable gain. And, the LTC2484 provides 24-bit resolution and includes the temperature sensor, but it does not have programmable gain.

All three parts are pin-compatible in 3- by 3-mm, 10-pin DFN packaging. Additionally, they're screened for commercial and industrial temperature ranges. Pricing begins at $1.85 each for the LTC2480, $1.65 each for the LTC2482, and $2.45 each for the LTC2484. All prices are based on quantities of 1000 pieces.

Linear Technology

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