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A/D Converter Houses Five Differential Reference Inputs

Milpitas, Calif. — Linear Technology Corp.'s LTC2447, a high accuracy, variable speed/resolution 24-bit delta-sigma analog-to-digital converter (A/D converter), features a unique multiplexing architecture to directly digitize multiple ratiometric sensors.

Four differential inputs, coupled with four differential reference inputs, allow ratiometric measurements of multiple resistance temperature detectors (RTDs), bridges and pressure sensors. A fifth differential reference can be shared by any or all inputs. This multiplexing architecture, combined with high accuracy and low drift, improve the performance while simplifying the analog front end of applications measuring temperature, pressure, flow, chromatography, weight, and general purpose data acquisition.

The LTC2447's flexible input multiplexer allows any combination of 8 single-ended or 4 differential inputs to be accurately digitized with either a dedicated reference input or a global reference input. The LTC2447's multiplexer outputs and A/D converter inputs are pinned out separately. This allows external signal chain components to be included within the calibration loop of the A/D converter, automatically removing offset and drift errors.

The fast 4-kHz multiplexing rate combined with the patented no latency delta-sigma architecture allows all 8-channels to be scanned in 2 ms, without the filter settling problems inherent in other delta-sigma converters. The LTC2447's programmable filter enables designers to tailor twenty different speed/resolution combinations to individual channels. For low output rate applications, the A/D converter provides 200 nV rms noise, which is equivalent to 500,000 counts on a ±50 mV sensor output (or 25 million counts on a full scale input) and simultaneous 50 Hz and 60 Hz line frequency noise rejection. At its fastest output rate, 8 kHz, the A/D converter provides over 17 effective bits.

For applications not requiring the signal chain calibration feature, the pin-compatible LTC2446 is available. The LTC2446/LTC2447 are offered in a 38-pin 5mm x 7mm QFN package, screened for industrial and commercial temperature ranges.

Pricing starts at $7.15 each for the LTC2446 and $7.15 each for the LTC2447 each in 1,000-piece quantities.

Summary of Features: LTC2446/LTC2447

  • LTC2447 — 24-Bit delta-sigma ADC with Automatic Signal Chain Calibration
  • LTC2446 — 24-Bit delta-sigma ADC
  • Five Differential Reference Inputs
  • 4-Channel Differential/8-Channel Single Ended Inputs
  • 6.9 Hz Output Rate, 200 nV rms Noise, Simultaneous 50/60 Hz Rejection
  • 3.5 μV rms Noise at 1.76 kHz Output Rate
  • Up to 8 kHz Output Rate
  • 5 ppm INL, No Missing Codes
  • 2.5 μV Offset Error
  • Transparent Auto Calibration on Input Signal Chain Components
  • Single Cycle Settling — Eliminates Digital Filter Setting Woes
  • Internal Oscillator —No External Components Required
  • Single 5-V Supply Operation
  • Tiny 38-Pin 5mm x 7mm QFN Package

    Data sheet for the LTC2447.

    For more company information, please visit: www.linear.com

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