Datasheet

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SBAS314B − APRIL 2004 − REVISED JANUARY 2009
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17
APPLICATIONS INFORMATION
GENERAL RECOMMENDATIONS
The ADS1222 is a high-resolution A/D converter.
Achieving optimal device performance requires careful
attention to the support circuitry and printed circuit
board (PCB) design. Figure 30 shows the basic
connections for the ADS1222. As with any precision
circuit, be sure to use good supply bypassing capacitor
techniques. A smaller value ceramic capacitor in
parallel with a larger value tantalum capacitor works
well. Place the capacitors, in particular the ceramic
ones, close to the supply pins. Use a ground plane and
tie the ADS1222 GND pin and bypass capacitors
directly to it. Avoid ringing on the digital inputs. Small
resistors (≈100Ω) in series with the digital pins can help
by controlling the trace impedance. Place these
resistors at the source end.
Pay special attention to the reference and analog
inputs. These are the most critical circuits. 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 reference such as the REF1004.
Often, only a simple RC filter is needed on the inputs.
This circuit limits the higher frequency noise. Avoid
low-grade dielectrics for the capacitors and place them
as close as possible to the input pins. Keep the traces
to the input pins short, and carefully watch how they are
routed on the PCB.
After the power supplies and reference voltage have
stabilized, issue a self-calibration command to
minimize offset and gain errors.
ADS1222
VDD
SCLK
CLK
DRDY/DOUT
MUX
TEMPEN
BUFEN
VREFP
VREFN
GND
AINN1
AINP1
AINN2
AINP2
100
Ω
100
Ω
100
Ω
100
Ω
100
Ω
100
Ω
Same as shown
for AINP1 and AINN1.
0.1
µ
F
10
µ
F
+5V
0.1
µ
F 10
µ
F
+2.5V Reference
220pF
0.1
µ
F
220pF
VIN
P
VIN
N
301Ω
301Ω
Figure 30. Basic Connections