LT1880 LINER [Linear Technology], LT1880 Datasheet - Page 10

• Manufacturer Part Number: LT1880
• Description: SOT-23, Rail-to-Rail Output, Picoamp Input Current Precision Op Amp
• Manufacturer: LINER [Linear Technology]

LT1880
APPLICATIO S I FOR ATIO
The transimpedance gain is set to 51.1k
feedback capacitor, C
response time is not an issue, or it may be selected for
maximally flat response and highest possible bandwidth
given a photodiode capacitance C
of C
Total output offset is below 262 V, worst-case, over
temperature (0 C–70 C). With a 5V output swing, this
guarantees a minimum 86dB dynamic range over
temperature (0 C–70 C), and a full-scale photodiode
current of 98 A.
Single-Supply Current Source for Platinum RTD
The precision, low bias current input stage of the LT1880
makes it ideal for precision integrators and current sources.
Figure 5 shows the LT1880 providing a simple precision
current source for a remote 1k
10
Figure 4. Feedback C
F
and rise time versus C
100
0.1
10
1
0.1
RISE TIME
U
1
F
C
, may be as large as desired where
F
F
and Rise Time vs Photodiode C
U
C
D
D
10
100mV OUTPUT STEP
(pF)
for maximally flat response.
D
. Figure 4 shows a chart
W
100
RTD on a 4-wire
1000
by R
U
F
D
. The
connection. The LT1634 reference places 1.25V at the
noninverting input of the LT1880, which then maintains its
inverting input at the same voltage by driving 1mA of
current through the RTD and the total 1.25k of resis-
tance set by R1 and R2. Imprecise components R4 and C1
ensure circuit stability, which would otherwise be exces-
sively dependant on the cable characteristics. R5 is also
noncritical and is included to improve ESD immunity and
decouple any cable capacitance from the LT1880’s output.
The 4-wire cable allows Kelvin sensing of the RTD voltage
while excluding the cable IR drops from the voltage
reading. With 1mA excitation, a 1k
across it at 0 C, and +3.85mV/ C temperature response.
This voltage can be easily read in myriad ways, with the
best method depending on the temperature region to be
emphasized and the particular ADC that will be reading the
voltage.
AT 0 C
RTD*
1k
Figure 5. Single Supply Current Source for Platinum RTD
*OMEGA F3141 1k , 0.1% PLATINUM RTD
R2
10
1%
180 , 5%
R1
1.24K
0.1%
1k, 5%
R5
R4
C1
0.1 F
LT1634ACS8
-1.25
150k, 1%
–
+
R3
LT1880
5V
V
+
–
OUT
5V
= 1.00V AT 0 C + 3.85mV/ C
RTD will have 1V
–50 C TO 600 C
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