AD8253ARMZ-R7 datasheet(18/24 Pages) AD

18 / 24 page

AD8253

Rev. 0 | Page 18 of 24

POWER SUPPLY REGULATION AND BYPASSING

The AD8253 has high PSRR. However, for optimal performance,

a stable dc voltage should be used to power the instrumentation

amplifier. Noise on the supply pins can adversely affect per-

formance. As in all linear circuits, bypass capacitors must be

used to decouple the amplifier.

Place a 0.1 μF capacitor close to each supply pin. A 10 μF tantalum

capacitor can be used farther away from the part (see Figure 55)

and, in most cases, it can be shared by other precision integrated

circuits.

AD8253

+VS

+IN

–IN

LOAD

REF

0.1µF

10µF

0.1µF

10µF

–VS

DGND

VOUT

DGND

Figure 55. Supply Decoupling, REF, and Output Referred to Ground

INPUT BIAS CURRENT RETURN PATH

The AD8253 input bias current must have a return path to its

local analog ground. When the source, such as a thermocouple,

cannot provide a return current path, one should be created

(see Figure 56).

THERMOCOUPLE

+VS

REF

–VS

AD8253

CAPACITIVELY COUPLED

+VS

REF

–VS

AD8253

TRANSFORMER

+VS

REF

–VS

AD8253

INCORRECT

CAPACITIVELY COUPLED

+VS

REF

–VS

AD8253

fHIGH-PASS = 2πRC

THERMOCOUPLE

+VS

REF

–VS

10MΩ

AD8253

TRANSFORMER

+VS

REF

–VS

AD8253

CORRECT

Figure 56. Creating an IBIAS Path

INPUT PROTECTION

All terminals of the AD8253 are protected against ESD. An external

resistor should be used in series with each of the inputs to limit

current for voltages greater than 0.5 V beyond either supply rail.

In such a case, the AD8253 safely handles a continuous 6 mA

current at room temperature. For applications where the AD8253

encounters extreme overload voltages, external series resistors

and low leakage diode clamps such as BAV199Ls, FJH1100s, or

SP720s should be used.

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