Very Low Noise, 24-Bit Analog-to-Digital Converter

FEATURES

• 24 Bits, No Missing Codes
  • All Data Rates and PGA Settings
    
• Up to 23 Bits Noise-Free Resolution
  
• ±0.0010% Nonlinearity (max)
  
• Data Output Rates to 30kSPS
  
• Fast Channel Cycling
  • 18.6 Bits Noise-Free (21.3 Effective Bits) at 1.45kHz
    
• One-Shot Conversions with Single-Cycle Settling
  
• Flexible Input Multiplexer with Sensor Detect
  • Four Differential Inputs (ADS1256 only)
  • Eight Single-Ended Inputs (ADS1256 only)
    
• Chopper-Stabilized Input Buffer
  
• Low-Noise PGA: 27nV Input-Referred Noise
  
• Self and System Calibration for All PGA Settings
  
• 5V Tolerant SPI^TM-Compatible Serial Interface
  
• Analog Supply: 5V
  
• Digital Supply: 1.8V to 3.6V
  
• Power Dissipation
  • As Low as 38mW in Normal Mode
  • 0.4mW in Standby Mode

APPLICATIONS

• Weigh Scales
  
• Scientific Instrumentation
  
• Industrial Process Control
  
• Medical Equipment
  
• Test and Measurement

DESCRIPTION

The ADS1255 and ADS1256 are extremely low-noise, 24-bit analog-to-digital (A/D) converters. They provide complete high-resolution measurement solutions for the most demanding applications.

The converter is comprised of a 4th-order, delta-sigma (∆Σ) modulator followed by a programmable digital filter. A flexible input multiplexer handles differential or single-ended signals and includes circuitry to verify the integrity of the external sensor connected to the inputs. The selectable input buffer greatly increases the input impedance and the low-noise programmable gain amplifier (PGA) provides gains from 1 to 64 in binary steps. The programmable filter allows the user to optimize between a resolution of up to 23 bits noise-free and a data rate of up to 30k samples per second (SPS). The converters offer fast channel cycling for measuring multiplexed inputs and can also perform one-shot conversions that settle in just a single cycle.

Communication is handled over an SPI-compatible serial interface that can operate with a 2-wire connection. Onboard calibration supports both self and system correction of offset and gain errors for all the PGA settings. Bidirectional digital I/Os and a programmable clock output driver are provided for general use. The ADS1255 is packaged in an SSOP-20, and the ADS1256 in an SSOP-28.

ABSOLUTE MAXIMUM RATINGS

over operating free-air temperature range unless otherwise noted⁽¹⁾

(1) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not implied.

PIN ASSIGNMENTS

SSOP PACKAGE (TOP VIEW)