Datasheet

Data Sheet AD8250
Rev. C | Page 17 of 24
POWER SUPPLY REGULATION AND BYPASSING
The AD8250 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 51)
and, in most cases, it can be shared by other precision integrated
circuits.
AD8250
+
V
S
+IN
–IN
LOAD
REF
0.1µF
10µF
0.1µF 10µF
–V
S
DGND
OUT
DGND
A0
A1
WR
06288-058
Figure 51. Supply Decoupling, REF, and Output Referred to Ground
INPUT BIAS CURRENT RETURN PATH
The AD8250 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 52).
THERMOCOUPLE
+V
S
REF
–V
S
AD8250
CAPACITIVELY COUPLED
+V
S
REF
C
C
–V
S
AD8250
TRANSFORMER
+V
S
REF
–V
S
AD8250
INCORRECT
CAPACITIVELY COUPLED
+V
S
REF
C
R
R
C
–V
S
AD8250
1
f
HIGH-PASS
=
2πRC
THERMOCOUPLE
+V
S
REF
–V
S
10MΩ
AD8250
TRANSFORMER
+V
S
REF
–V
S
AD8250
CORRECT
06288-059
Figure 52. Creating an I
BIAS
Return Path
INPUT PROTECTION
All terminals of the AD8250 are protected against ESD. Note
that 2.2 kΩ series resistors precede the ESD diodes as shown in
Figure 47. The resistors 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 input to limit current for voltages greater
than 13 V beyond either supply rail. In either scenario, the
AD8250 safely handles a continuous 6 mA current at room
temperature. For applications where the AD8250 encounters
extreme overload voltages, external series resistors and low
leakage diode clamps, such as BAV199Ls, FJH1100s, or SP720s,
should be used.