AD8275
POWER SUPPLIES
COMMON-MODE INPUT VOLTAGE RANGE
Use a stable dc voltage to power the AD8275. Noise on the
supply pins can adversely affect performance. Place a bypass
capacitor of 0.1 µF between each supply pin and ground, as
close to each pin as possible. A tantalum capacitor of 10 µF
should also be used between each supply and ground. It can
be farther away from the AD8275 and typically can be shared
by other precision integrated circuits.
The common-mode voltage range is a function of the input
voltage range of the internal op amp, the supply voltage, and
the reference voltage.
Equation 1 expresses the maximum positive common-mode
voltage range.
VCM_POS ≤ 13.14(+VS) – 7.14(–VS) – 5((REF1 + REF2)/2) – 29.69 (1)
Equation 2 expresses the minimum common-mode voltage
range.
REFERENCE
The reference terminals are used to provide a bias level for the
output. For example, in a single-supply 5 V operation, the
reference terminals can be set so that the output is biased at
2.5 V. This ensures that the output can swing positive or
negative around a 2.5 V level.
VCM_NEG ≥ 6(–VS) – 5((REF1 + REF2)/2) – 0.11
(2)
The voltage range of the internal op amp varies depending on
temperature. The equations reflect a typical input voltage range
of +VS − 0.9 V and −VS + 1.35 V over temperature. Table 5 lists
expected common-mode ranges for typical configurations.
Figure 33 and Figure 34 illustrate two different ways to set the
reference voltage. See the Basic Connection section for the
differences between the two settings.
Table 5. Expected Common-Mode Voltage Range for Typical
Configurations
+VS (V)1 VREF1 (V)
VREF2 (V)
VCM+ (V) VCM− (V)
The allowable reference voltage range is a function of the
common-mode input and supply voltages. The REF1 and REF2
pins should not exceed either +VS or −VS by more than 0.5 V.
5
5
5
3.3
3.3
5
5
5
5
5
5
5
5
0
0
0
0
0
5
23.5
29.8
25.8
5.4
−12.6
−6.4
−10.4
−8.4
2.5
4.096
3.3
2.5
5
4.096
3
2.5
2.048
1.25
0
The REFx terminals should be driven by low source impedance
because parasitic resistance in series with REF1 and REF2 can
adversely affect CMRR and gain accuracy.
7.4
−6.4
11.0
15.5
21.0
23.5
25.8
29.8
36.0
−25.1
−20.6
−15.1
−12.6
−10.4
−6.4
CORRECT
INCORRECT
4.096
3
2.5
2.048
1.25
0
+V
7
+V
7
S
S
SENSE
SENSE
50kΩ
–IN
10kΩ
50kΩ
–IN
10kΩ
2
3
5
2
3
5
OUT
OUT
6
6
V
REF
−0.1
V
REF
1 –VS = 0 V.
REF2
REF1
REF2
REF1
50kΩ
+IN
50kΩ
+IN
20kΩ
20kΩ
20kΩ
20kΩ
8
1
8
1
INPUT PROTECTION
–V
S
4
–V
S
The inputs of the AD8275, +IN and −IN, are protected by ESD
diodes that clamp 40 V above −VS and 40 V below +VS. When
operating on a single +5 V supply, the ESD diode conducts at
input voltages less than −35 V and greater than +40 V.
AD8275
AD8275
4
+V
7
+V
7
S
S
If the input voltage is expected to exceed the maximum ratings
of the AD8275, use external transorbs. Adding series resistors to
the inputs of the AD8275 is not recommended because the
internal resistor ratios are matched to provide optimal CMRR
and gain accuracy. Adding external series resistors to the input
degrades the performance of the AD8275.
SENSE
SENSE
10kΩ
50kΩ
–IN
10kΩ
50kΩ
IN
2
3
5
2
3
5
–
OUT
OUT
6
6
V
REF
V
REF
REF2
REF1
R
EF2
50kΩ
+IN
50kΩ
20kΩ
20kΩ
20kΩ
8
1
8
1
+IN
REF1
20kΩ
–V
All other pins are protected by ESD diodes that clamp 0.5 V
beyond either supply rail. For example, the voltage range of the
REF1 and REF2 pins on a 5 V supply is −0.5 V to +5.5 V.
–V
S
S
AD8275
AD8275
4
4
Figure 35. REF1 and REF2 Pin Guidelines
Rev. A | Page 12 of 16
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