Datasheet

SMALL INPUT SIGNALS
ADS1225
VREFP
VREFN
START
DRDY/DOUT
AVDD DVDD
GND
AINP1
MSP430xxx
or Cm
GND
+5V
+5V
+5V
RF
4.99kW
RF
4.99kW
RG
100W
0.22 Fm
1kW
10 Fm
0.1 Fm
0.1 Fm
LoadCell
AINN1
1kW
+3V
+3V
0.1 Fm
0.1 Fm
0.1 Fm
SCLK
1/2
OPA2333
1/2
OPA2333
G=1+
2R
F
R
G
MODE
TEMPEN
BUFEN
Uselow-driftresistors
forR andR
F G
ADS1225
ADS1226
SBAS346C – MAY 2006 – REVISED JANUARY 2009 ....................................................................................................................................................... www.ti.com
measurement of approximately 1V while keeping the
noise contribution of the OPA2333 low. The noise is
Figure 32 shows the schematic of the ADS1225 for
low enough compared to full-scale to create a
measuring small output signals such as the output of
several-thousand count weigh scale, even in
a bridge sensor or load cell. In this application, the
High-Speed mode. For better accuracy, this noise
load cell is combined with the ADS1225 and an
could be lowered through either additional filtering or
MSP430 microcontroller. An OPA2333 is used to
using the High-Resolution mode.
buffer the inputs and to provide the gain of the load
cell signal. A 5V source is used as the reference and It is important to make sure that the reference and
the excitation, although any clean source can create inputs are clean from clocks or other periodic signals
a proper ratiometric signal for the reference. to prevent coupling. Isolate the analog from the digital
supplies and grounds whenever possible.
A typical load cell with a bridge sensitivity of 2mV/V
using a 5V source would have a full-scale output of
10mV. The recommended gain of the OPA2333, for
this load cell using low-drift resistors, would be 1 +
2R
F
/R
G
= 100.8V/V. This value gives a full-scale
Figure 32. Using the OPA2333 as a Gain Stage in Front of the ADS1225
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Product Folder Link(s): ADS1225 ADS1226