AD8222 Analog Devices, AD8222 Datasheet - Page 17

• Manufacturer Part Number: AD8222
• Description: Precision, Dual-Channel Instrumentation Amplifier Data Sheet (Rev. 0, 7/2006)
• Manufacturer: Analog Devices

The AD8222 should be decoupled with 0.1 μF bypass capacitors,
one for each supply. The positive supply decoupling capacitor
should be placed near Pin 16, and the negative supply
decoupling capacitor should be placed near Pin 8. Each supply
should also be decoupled with a 10 μF tantalum capacitor. The
tantalum capacitor can be placed further away from the
AD8222 and can generally be shared by other precision integrated
circuits. Figure 46 shows an example layout.
SOLDER WASH
The solder process can leave flux and other contaminants on
the board. When these contaminants are between the AD8222
leads and thermal pad, they can create leakage paths that are
larger than the AD8222’s bias currents. A thorough washing
process removes these contaminants and restores the AD8222’s
excellent bias current performance.
INPUT BIAS CURRENT RETURN PATH
The input bias current of the AD8222 must have a return path
to common. When the source, such as a thermocouple, cannot
provide a return current path, one should be created, as shown
in Figure 47.
R
G
0.1µF
1
2
3
4
Figure 46. Example Layout
AD8222
16
5
15
6
14
7
0.1µF
13
8
12
11
10
9
R
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G
INPUT PROTECTION
All terminals of the AD8222 are protected against ESD (1 kV—
human body model). In addition, the input structure allows for
dc overload conditions of about 2½ V beyond the supplies.
Input Voltages Beyond the Rails
For larger input voltages, an external resistor should be used in
series with each input to limit current during overload conditions.
The AD8222 can safely handle a continuous 6 mA current. The
limiting resistor can be computed from
For applications where the AD8222 encounters extreme overload
voltages, such as cardiac defibrillators, external series resistors
and low leakage diode clamps, such as the BAV199L, the FJH1100s,
or the SP720, should be used.
CAPACITIVELY COUPLED
C
C
R
THERMOCOUPLE
TRANSFORMER
LIMIT
INCORRECT
AD8222
+V
–V
AD8222
AD8222
≥
+V
–V
+V
–V
S
S
V
S
S
S
S
IN
6
−
REF
Figure 47. Creating an I
mA
V
REF
REF
SUPPLY
f
HIGH-PASS
−
400
Ω
=
CAPACITIVELY COUPLED
2πRC
1
10MΩ
BIAS
C
C
Path
R
R
THERMOCOUPLE
TRANSFORMER
CORRECT
AD8222
AD8222
AD8222
+V
+V
+V
–V
–V
–V
AD8222
S
S
S
S
S
S
REF
REF
REF