Features

• Five Selectable Differential Reference Inputs
• Four Differential/Eight Single-Ended Inputs
• 4-Way MUX for Multiple Ratiometric
• Measurements
• Up to 8kHz Output Rate
• Up to 4kHz Multiplexing Rate
• Selectable Speed/Resolution:
  2µV_RMS Noise at 1.76kHz Output Rate
  200nV_RMS Noise at 13.8Hz Output Rate with
  Simultaneous 50/60Hz Rejection
• Guaranteed Modulator Stability and Lock-Up Immunity for any Input and Reference Conditions
• 0.0005% INL, No Missing Codes
• Autosleep Enables 20µA Operation at 6.9Hz
• <5µV Offset (4.5V < V_CC < 5.5V, –40°C to 85°C)
• Differential Input and Differential Reference with GND to V_CC Common Mode Range
• No Latency Mode, Each Conversion is Accurate Even After a New Channel is Selected
• Internal Oscillator—No External Components
• LTC2447 Includes MUXOUT/ADCIN for External Buffering or Gain
• Tiny QFN 5mm x 7mm Package

Typical Application

Description

The LTC2446/LTC2447 4-terminal switching enables multiplexed ratiometric measurements. Four sets of selectable differential inputs coupled with four sets of differential reference inputs allow multiple RTDs, bridges and other sensors to be digitized by a single converter. A fifth differential reference input can be selected for any input channel not requiring ratiometric measurements (thermocouples, voltages, current sense, etc.). The flexible input multiplexer allows single-ended or differential inputs coupled with a slaved reference input or a universal reference input.

A proprietary delta-sigma architecture results in absolute accuracy (offset, full-scale, linearity) of 15ppm, noise as low as 200nV_RMS and speeds as high as 8kHz. Through a simple 4-wire interface, ten speed/resolution combinations can be selected. The first conversion following a speed, resolution, channel change or reference change is valid since there is no settling time between conversions, enabling scan rates of up to 4kHz. Additionally, a 2x mode can be selected for any speed-enabling output rates up to 8kHz with one cycle of latency.

Protected by U.S. Patents, including 6140950, 6169506, 6208279, 6411242, 6639526