8170FSZ 查看數據表（PDF） - Intersil
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8170FSZ Datasheet PDF : 14 Pages
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VIN/2
VIN/2
VCM
RG
+2.4V TO +5.5V
71
3 IN+
V+ EN
+
2 IN-
-
8 FB+ EL8170/3
6
+
5 FB- -
V-
4
RF
EL8170, EL8173
EN
VOUT
VIN/2
VIN/2
+2.4V TO +5.5V
VCM
R1
REF
R2 RG
+2.4V TO +5.5V
71
3 IN+
V+ EN
+
2 IN-
- EL8170, 6
8
FB+
+
EL8173
5 FB- -
V-
4
RF
EN
VOUT
FIGURE 39. GAIN IS SET BY TWO EXTERNAL RESISTORS,
RF AND RG
VOUT
=
⎛
⎜
⎝
1
+
R-R----G-F--⎠⎟⎞
VIN
(EQ. 1)
In Figure 39, the FB+ pin and one end of resistor RG are
connected to GND. With this configuration, Equation 1 is only
true for a positive swing in VIN; negative input swings will be
ignored and the output will be at ground.
Reference Connection
Unlike a three op amp instrumentation amplifier, a finite
series resistance seen at the REF terminal does not degrade
the EL8170 and EL8173's high CMRR performance,
eliminating the need for an additional external buffer
amplifier. The circuit shown in Figure 40 uses the FB+ pin as
a REF terminal to center or to adjust the output. Because the
FB+ pin is a high impedance input, an economical resistor
divider can be used to set the voltage at the REF terminal.
The reference voltage error due to the input bias current is
minimized by keeping the values of the voltage divider
resistors, R1 and R2, as low as possible. Any voltage applied
to the REF terminal will shift VOUT by VREF times the closed
loop gain, which is set by resistors RF and RG according to
Equation 2. Note that any noise or unwanted signals on the
reference supply will be amplified at the output according to
Equation 2.
VOUT
=
⎛
⎜1
⎝
+
R-R----G-F--⎠⎟⎞
(VIN)
+
⎛
⎜1
⎝
+
R-R----G-F--⎠⎟⎞
(VREF)
(EQ. 2)
FIGURE 40. GAIN SETTING AND REFERENCE CONNECTION
The FB+ pin can also be connected to the other end of
resistor, RG. See Figure 41. Keeping the basic concept that
the EL8170 and EL8173 in-amps maintain constant
differential voltage across the input terminals and feedback
terminals (IN+ - IN- = FB+ - FB-), the transfer function of
Figure 41 can be derived (Equation 3). Note that the VREF
gain term is eliminated, and susceptibility to external noise is
reduced.
VIN/2
VIN/2
VCM
+2.4V TO +5.5V
71
3 IN+
V+ EN
+
2 IN- - EL8170,
6
8 FB+ EL8173
+
5 FB-
-
V-
4
EN
VOUT
VREF
RG
RF
FIGURE 41. REFERENCE CONNECTION WITH AN AVAILABLE
VREF
VOUT
=
⎛
⎜
⎝
1
+
R-R----G-F--⎠⎟⎞
(VIN
)
+
(
VREF
)
(EQ. 3)
12
FN7490.4
February 14, 2008
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