24-Bit High Speed 8-/16-Channel ∆∑ ADCs with Selectable Speed/Resolution

The LTC2444/LTC2445/LTC2448/LTC2449 are 8-/16- channel (4-/8-differential) high speed 24-bit No Latency ∆∑ ADCs. They use a proprietary delta-sigma architecture enabling variable speed/resolution. Through a simple 4-wire serial interface, ten speed/resolution combinations 6.9Hz/280nVRMS to 3.5kHz/25µVRMS (4kHz with external oscillator) can be selected with no latency between conversion results or shift in DC accuracy (offset, full-scale, linearity, drift). Additionally, a 2X speed mode can be selected enabling output rates up to 7kHz (8kHz if an external oscillator is used) with one cycle latency.

Any combination of single-ended or differential inputs can be selected with a common mode input range from ground to VCC, independent of VREF. While operating in the 1X speed mode the first conversion following a new speed, resolution, or channel selection is valid. Since there is no settling time between conversions, all 8 differential channels can be scanned at a rate of 500Hz. At the conclusion of each conversion, the converter is internally reset eliminating any memory effects between successive conversions and assuring stability of the high order delta-sigma modulator.

Applications

* High Speed Multiplexing

* Weight Scales

* Auto Ranging 6-Digit DVMs

* Direct Temperature Measurement

* High Speed Data Acquisition

* Up to 8 Differential or 16 Single-Ended Input Channels

* Up to 8kHz Output Rate

* Up to 4kHz Multiplexing Rate

* Selectable Speed/Resolution

* 2µVRMS Noise at 1.76kHz Output Rate

* 200nVRMS 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 < VCC < 5.5V, –40°C to 85°C)

* Differential Input and Differential Reference with GND to VCC Common Mode Range

* No Latency Mode, Each Conversion is Accurate Even After a New Channel is Selected

* Internal Oscillator-No External Components

* LTC2445/LTC2449 Include MUXOUT/ADCIN for External Buffering or Gain

* Tiny QFN 5mm x 7mm Package