LT1880 데이터 시트보기 (PDF) - Linear Technology
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LT1880 Datasheet PDF : 12 Pages
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APPLICATIONS INFORMATION
LT1880
VREF
RG
VIN
+
–
RF
VIN
+
–
RF
VIN
+
–
RG
VREF
INVERTING: AV = –RF/RG
OP AMP INPUTS DO NOT MOVE,
BUT ARE FIXED AT DC BIAS
POINT VREF
INPUT DOES NOT HAVE TO BE
RAIL-TO-RAIL
NONINVERTING: AV = 1 +RF/RG
INPUTS MOVE BY AS MUCH AS
VIN, BUT THE OUTPUT MOVES
MORE
INPUT MAY NOT HAVE TO BE
RAIL-TO-RAIL
NONINVERTING: AV = +1
INPUTS MOVE AS MUCH AS
OUTPUT
INPUT MUST BE
RAIL-TO-RAIL FOR OVERALL
CIRCUIT RAIL-TO-RAIL
PERFORMANCE
1880 F01
Figure 1. Some Op Amp Configurations Do Not Require
Rail-to Rail Inputs to Achieve Rail-to-Rail Outputs
The circuit of Figure 2 shows an extreme example of the
inverting case. The input voltage at the 1M resistor can
swing ±13.5V and the LT1880 will output an inverted,
divided-by-ten version of the input voltage. The input
accuracy is limited by the resistors to 0.2%. Output
referred, this error becomes 2.7mV. The 40μV input offset
voltage contribution, plus the additional error due to input
bias current times the ~100k effective source impedance,
contribute only negligibly to error.
±13.5V SWINGS
WELL OUTSIDE
SUPPLY RAILS
VIN
1M, 0.1%
1.5V
+
LT1880
–
±1.35V
OUTPUT
SWING
100k, 0.1%
–1.5V
1880 F02
Figure 2. Extreme Inverting Case: Circuit Operates Properly with
Input Voltage Swing Well Outside Op Amp Supply Rails.
Precision Photodiode Amplifier
Photodiode amplifiers usually employ JFET op amps be-
cause of their low bias current; however, when precision
is required, JFET op amps are generally inadequate due to
their relatively high input offset voltage and drift. The
LT1880 provides a high degree of precision with very low
bias current (IB = 150pA typical) and is therefore appli-
cable to this demanding task. Figure 3 shows an LT1880
configured as a transimpedance photodiode amplifier.
WORST-CASE
OUTPUT OFFSET
≤196μV AT 25°C
≤262μV 0°C TO 70°C
≤323μV –40°C TO 85°C
CF
RF 51.1k
5V
–
PHOTODIODE
(SEE TEXT)
CD
LT1880
+
OUT
–5V
1880 F02
Figure 3. Precision Photodiode Amplifier
1880fa
9
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