Delta-Sigma ADC features differential input current cancellation

Dec 7, 2006 11:15 AM

Linear Technology’s LTC2499 is a 16-channel delta-sigma ADC that communicates via an I²C-compatible serial interface and includes a unique analog input architecture. The LTC2499's Easy Drive front-end design results in zero average differential input current, allowing measurements of high impedance sources without the use of an internal buffer. This sampling scheme simplifies the design of front-end signal conditioning circuits and allows the ADC to be driven directly from bridges, RTDs, thermocouplers and high-impedance sensors. Rail-to-rail input signals can be directly digitized while maintaining excellent dc accuracy (2 ppm INL).

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The LTC2499 includes a high-accuracy internal temperature sensor that offers 0.03°C resolution and 2°C absolute accuracy. The ADC converts the output of the temperature sensor or the input multiplexer, which can be configured for 16 single-ended channels, eight differential channels, or combinations of both. After a new channel is selected, the LTC2499's No Latency Delta-Sigma digital filter settles in a single cycle.

The LTC2499 performs conversions at rates of 15 Hz or 7.5 Hz while using the internal oscillator and can be configured to reject line frequencies of 50 Hz, 60 Hz or simultaneous 50 Hz/60 Hz, while maintaining 600 nV_RMS noise across the full input voltage range. Three address-select pins allow 27 unique address combinations, in addition to a separate global address for synchronizing multiple devices.

The LTC2497 is a pin-compatible 16-bit ADC for lower-resolution applications. The LTC2499 and LTC2497 are each available in QFN-38 (5 mm x 7 mm) packages, offering a pin-compatible and code-compatible family for performance/cost optimization. The LTC2498 and LTC2496 are equivalent 24-bit and 16-bit Easy Drive ADCs that communicate via a 4-wire SPI-compatible interface.

Both the LTC2499 and LTC2497 are available in commercial and industrial temperature ranges. Pricing begins at $3.45 each for the LTC2499 and $2.65 each for the LTC2497, both in 1000-piece quantities.