Datasheet

OVERVIEW ANALOG INPUTS (AINx+, AINx – )
MUX
SerialInterface
Oscillator
DS
ADC
VREFP VREFN
Buffer
MUX
ADS1226Only
AINP1
AINN1
AINP
AINN
AINP2
AINN2
DRDY/DOUT
SCLK
TEMPEN
START
MODE
BUFEN
V
IN
S
S
V
REF
ADS1225
ADS1226
SBAS346C – MAY 2006 – REVISED JANUARY 2009 ....................................................................................................................................................... www.ti.com
The ADS1225 and ADS1226 are 24-bit delta-sigma The input signal to be measured is applied to the
A/D converters. Figure 19 shows a conceptual input pins AINPx and AINNx. The positive internal
diagram of the device. The ADS1225 has a single input is generalized as AINP, and the negative
channel, while the ADS1226 allows for one of two internal input is generalized as AINN. The signal is
input channels to be selected through a multiplexer. A selected though the input MUX, which is controlled by
buffer can also be selected to increase the input MUX, as shown in Table 1 . The ADS1225 and
impedance. The modulator measures the differential ADS1226 accept differential input signals, but can
input signal V
IN
= (AINP – AINN) against the also measure unipolar signals. When measuring
differential reference V
REF
= (VREFP – VREFN). The unipolar (or single-ended) signals with respect to
full-scale input range is ± V
REF
. A 2-wire serial ground, connect the negative input (AINN) to ground
interface indicates conversion completion and and connect the input signal to the positive input
provides the user with the output data. An internal (AINP). Note that when the ADS1225 and ADS1226
oscillator allows for free-running of the ADS1225 and are configured this way, only half of the converter
ADS1226. full-scale range is used since only positive digital
output codes are produced. An input buffer can be
Two other pins are used to control the operation of
selected to increase the input impedance of the A/D
the ADS1225 and ADS1226. The START pin initiates
converter with the BUFEN pin.
conversions. The MODE pin puts the device into one
of two modes. In High-Speed mode, the device gives
Table 1. Input Channel Selection with MUX
data at 100 samples per second (SPS). In
DIGITAL PIN SELECTED ANALOG INPUTS
High-Resolution mode, data comes out at 16SPS with
lower noise. In both modes, the device has
MUX POSITIVE INPUT NEGATIVE INPUT
single-cycle settling, reducing the latency of the
0 AINP1 AINN1
output data.
1 AINP2 AINN2
Figure 19. Conceptual Diagram of the ADS1225 and ADS1226
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