ADS1255IDB Burr-Brown Corporation, ADS1255IDB Datasheet - Page 11

• Manufacturer Part Number: ADS1255IDB
• Description: Very Low Noise/ 24-Bit Analog-to-Digital Converter
• Manufacturer: Burr-Brown Corporation

OVERVIEW
The ADS1255 and ADS1256 are very low-noise A/D
converters. The ADS1255 supports one differential or two
single-ended inputs and has two general-purpose digital
I/Os. The ADS1256 supports four differential or eight
single-ended inputs and has four general-purpose digital
I/Os. Otherwise, the two units are identical and are
referred to together in this data sheet as the ADS1255/6.
Figure 5 shows a block diagram of the ADS1256. The
input multiplexer selects which input pins are connected to
the A/D converter. Selectable current sources within the
input multiplexer can check for open- or short-circuit
conditions on the external sensor. A selectable onboard
input buffer greatly reduces the input circuitry loading by
providing up to 80M
provides a gain of 1, 2, 4, 8, 16, 32, or 64. The ADS1255/6
converter is comprised of a 4th-order, delta-sigma
modulator followed by a programmable digital filter.
www.ti.com
AINCOM
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
Multiplexer
Sensor
Detect
Input
and
of impedance. A low-noise PGA
AIN
AIN
P
N
Buffer
PGA
1:64
Figure 5. Block Diagram
V
IN
PGA
The modulator measures the amplified differential input
signal, V
reference, V
reference is scaled internally by a factor of two so that the
full-scale input range is 2V
The digital filter receives the modulator signal and
provides a low-noise digital output. The data rate of the
filter is programmable from 2.5SPS to 30kSPS and allows
tradeoffs between resolution and speed.
Communication is done over an SPI-compatible serial
interface with a set of simple commands providing control of
the ADS1255/6. Onboard registers store the various settings
for the input multiplexer, sensor detect current sources, input
buffer enable, PGA setting, data rate, etc. Either an external
crystal or clock oscillator can be used to provide the clock
source. General-purpose digital I/Os provide static read/write
control of up to four pins. One of the pins can also be used
to supply a programmable clock output.
VREFP VREFN
ADS1256
4th−Order
Modulator
D3 D2
Only
Digital I/O
Purpose
General
2
V
2V
REF
IN
REF
D1 D0/CLKOUT
REF
= (AIN
Programmable
Digital Filter
Converter
= (VREFP − VREFN). The differential
A/D
SBAS288D − JUNE 2003 − REVISED AUGUST 2004
P
– AIN
REF
Generator
N
Interface
Control
), against the differential
Serial
Clock
SPI
(for PGA = 1).
XTAL1/CLKIN
XTAL2
RESET
SYNC/PDWN
DRDY
SCLK
DIN
DOUT
CS
ADS1255
ADS1256
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