ad8251nbsp Analog Devices, Inc., ad8251nbsp Datasheet - Page 18

• Manufacturer Part Number: ad8251nbsp
• Description: 10 Mhz, 20 V/?s, G = 1, 2, 4, 8 I Cmos Programmable Gain Instrumentation Amplifier
• Manufacturer: Analog Devices, Inc.

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.
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).
Figure 53. Supply Decoupling, REF, and Output Referred to Ground
DGND
+IN
–IN
AD8251
+V
–V
S
WR
S
DGND
A1
0.1µF
0.1µF
A0
REF
10µF
10µF
LOAD
V
OUT
Rev. 0 | Page 18 of 24
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.
CAPACITIVELY COUPLED
C
C
THERMOCOUPLE
TRANSFORMER
INCORRECT
AD8251
+V
–V
AD8251
AD8251
+V
–V
+V
–V
S
S
S
S
S
S
Figure 54. Creating an I
REF
REF
REF
f
HIGH-PASS
CAPACITIVELY COUPLED
=
2πRC
10MΩ
1
BIAS
C
C
THERMOCOUPLE
Path
TRANSFORMER
R
R
CORRECT
AD8251
AD8251
AD8251
+V
–V
+V
–V
+V
–V
S
S
S
S
S
S
REF
REF
REF