AD623 datasheet(17/24 Pages) AD

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AD8222

Rev. 0 | Page 17 of 24

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.

AD8222

0.1µF

Figure 46. 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.

THERMOCOUPLE

+VS

REF

–VS

AD8222

CAPACITIVELY COUPLED

+VS

REF

–VS

AD8222

TRANSFORMER

+VS

REF

–VS

AD8222

INCORRECT

CAPACITIVELY COUPLED

+VS

REF

–VS

AD8222

fHIGH-PASS = 2πRC

THERMOCOUPLE

+VS

REF

–VS

10MΩ

AD8222

TRANSFORMER

+VS

REF

–VS

AD8222

CORRECT

Figure 47. Creating an IBIAS Path

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

400

−

≥

SUPPLY

LIMIT

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.

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