AD8251_07 Datasheet, PDF (18/24 Pages) Analog Devices – 10 MHz, 20 V/μs, G = 1, 2, 4, 8 i CMOS® Programmable Gain Instrumentation Amplifier

AD8251
POWER SUPPLY REGULATION AND BYPASSING
The AD8251 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 tanta-
lum capacitor can be used farther away from the part (see
Figure 53) and, in most cases, it can be shared by other
precision integrated circuits.
+V_S
0.1µF
WR
A1
+IN
A0
10µF
AD8251
–IN
REF
DGND
V_OUT
LOAD
0.1µF
10µF
DGND
–V_S
Figure 53. Supply Decoupling, REF, and Output Referred to Ground
INPUT BIAS CURRENT RETURN PATH
The AD8251 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 54).
INCORRECT
+V_S
CORRECT
+V_S
AD8251
REF
–V_S
TRANSFORMER
+V_S
AD8251
REF
–V_S
TRANSFORMER
+V_S
AD8251
REF
–V_S
THERMOCOUPLE
+V_S
C
AD8251
REF
10MΩ
–V_S
THERMOCOUPLE
+V_S
C
AD8251
f_HIGH-PASS
=
1
2πRC
R
AD8251
C
REF
C
REF
R
–V_S
–V_S
CAPACITIVELY COUPLED
CAPACITIVELY COUPLED
Figure 54. Creating an IBIAS Path
INPUT PROTECTION
All terminals of the AD8251 are protected against ESD. Note
that 2.2 kΩ series resistors precede the ESD diodes as shown in
Figure 49. They limit current into the diodes and allow for dc
overload conditions 13 V above the positive supply and 13 V
below the negative supply. An external resistor should be used
in series with each of the inputs to limit current for voltages
greater than 13 V beyond either supply rail. In either scenario,
the AD8251 safely handles a continuous 6 mA current at room
temperature. For applications where the AD8251 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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