SBAS288D − JUNE 2003 − REVISED AUGUST 2004
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FEATURES
C0068 24 Bits, No Missing Codes
− All Data Rates and PGA Settings
C0068 Up to 23 Bits Noise-Free Resolution
C0068 ±0.0010% Nonlinearity (max)
C0068 Data Output Rates to 30kSPS
C0068 Fast Channel Cycling
− 18.6 Bits Noise-Free (21.3 Effective Bits)
at 1.45kHz
C0068 One-Shot Conversions with Single-Cycle
Settling
C0068 Flexible Input Multiplexer with Sensor Detect
− Four Differential Inputs (ADS1256 only)
− Eight Single-Ended Inputs (ADS1256 only)
C0068 Chopper-Stabilized Input Buffer
C0068 Low-Noise PGA: 27nV Input-Referred Noise
C0068 Self and System Calibration for All PGA
Settings
C0068 5V Tolerant SPI-Compatible Serial Interface
C0068 Analog Supply: 5V
C0068 Digital Supply: 1.8V to 3.6V
C0068 Power Dissipation
− As Low as 38mW in Normal Mode
− 0.4mW in Standby Mode
APPLICATIONS
C0068 Weigh Scales
C0068 Scientific Instrumentation
C0068 Industrial Process Control
C0068 Medical Equipment
C0068 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.
All trademarks are the property of their respective owners.
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Copyright  2003−2004, Texas Instruments Incorporated
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.
XTAL2
Serial
Interface
Mux
and
Sensor
Detect
Programmable
Digital Filter
4th−Order
Modulator
VREFP VREFN
ADS
1
2
5
6
O
n
l
y
ADS1256
Only
Buffer
AVDD DVDD
1:64
DGNDD3 D2 D1 D0/CLKOUTAGND
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AINCOM
XTAL1/CLKIN
RESET
DRDY
SCLK
DIN
SYNC/PDWN
CS
DOUT
Control
General
Purpose
Digital I/O
Clock
Generator
PGA