Datasheet

APPLICATION INFORMATION
EXPOSED THERMAL PAD
GENERAL RECOMMENDATIONS
ADS1226
START
SCLK
DRDY/DOUT
BUFEN
GND
AINN1
AINP1
AINN2
1
2
3
4
12
11
10
9
100W
100W
100W
100W
100W
100W
100W
Sameasshown
forAINP1andAINN1.
10 Fm
16 15
AVDD DVDD VREFP VREFN
TEMPEN
MUX
MODE
AINP2
0.1 Fm
0.1 Fm
+5V
+3V
10 Fm
14 13
5 6 7 8
0.1 Fm
REF1004
301W
220pF
0.1 Fm
220pF
301W
ADS1225
ADS1226
www.ti.com ....................................................................................................................................................... SBAS346C – MAY 2006 – REVISED JANUARY 2009
ADS1226 GND pin and bypass capacitors directly to
it. Avoid ringing on the digital inputs. Small resistors
The exposed thermal pads of the ADS1225 and
( ≈ 100 Ω ) in series with the digital pins can help by
ADS1226 are internally connected to GND. To protect
controlling the trace impedance. Place these resistors
the package from board stress, solder the exposed
at the source end.
thermal pad to the printed circuit board (PCB) and
leave it floating electrically. For further information, Pay special attention to the reference and analog
see Application Report SLAU271 , QFN/SON PCB inputs. These inputs are critical to performance.
Attachment, available for download from www.ti.com . Bypass the voltage reference using similar
techniques to the supply voltages. The quality of the
reference directly affects the overall accuracy of the
device. Make sure to use a low noise and low drift
The ADS1225 and ADS1226 are high-resolution A/D
reference such as the REF1004 . Often, only a simple
converters. Achieving optimal device performance
RC filter is needed on the inputs. The circuit limits the
requires careful attention to the support circuitry and
higher frequency noise. Avoid low-grade dielectrics
PCB design. Figure 31 shows the basic connections
for the capacitors and place them as close as
for the ADS1225 and ADS1226. As with any
possible to the input pins. Keep the traces to the
precision circuit, be sure to use good supply
input pins short, and carefully watch how they are
bypassing capacitor techniques. A smaller value
routed on the PCB.
ceramic capacitor in parallel with a larger value
After the power supplies and reference voltage have
tantalum capacitor works well. Place the capacitors,
stabilized, issue a self-calibration command to
in particular the ceramic ones, close to the supply
minimize offset and gain errors.
pins. Use a ground plane and tie the ADS1225 and
Figure 31. Basic Connections
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Product Folder Link(s): ADS1225 ADS1226