Datasheet LT1880 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | SOT-23, Rail-to-Rail Output, Picoamp Input Current Precision Op Amp |
| Pages / Page | 12 / 10 — APPLICATIONS INFORMATION. Single-Supply Current Source for Platinum RTD |
| File Format / Size | PDF / 233 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Single-Supply Current Source for Platinum RTD
Model Line for this Datasheet
Text Version of Document
LT1880
APPLICATIONS INFORMATION
The transimpedance gain is set to 51.1kΩ by RF. The connection. The LT1634 reference places 1.25V at the feedback capacitor, CF, may be as large as desired where noninverting input of the LT1880, which then maintains response time is not an issue, or it may be selected for its inverting input at the same voltage by driving 1mA maximally flat response and highest possible bandwidth of current through the RTD and the total 1.25kΩ of given a photodiode capacitance CD. Figure 4 shows a resistance set by R1 and R2. Imprecise components R4 chart of CF and rise time versus CD for maximally flat and C1 ensure circuit stability, which would otherwise be response. Total output offset is below 262μV, worst-case, excessively dependant on the cable characteristics. R5 is over temperature (0°C to 70°C). With a 5V output swing, also noncritical and is included to improve ESD immunity this guarantees a minimum 86dB dynamic range over and decouple any cable capacitance from the LT1880’s temperature (0°C to 70°C), and a full-scale photodiode output. The 4-wire cable allows Kelvin sensing of the RTD current of 98μA. voltage while excluding the cable IR drops from the voltage reading. With 1mA excitation, a 1kΩ RTD will have 1V
Single-Supply Current Source for Platinum RTD
across it at 0°C, and +3.85mV/°C temperature response. The precision, low bias current input stage of the LT1880 This voltage can be easily read in myriad ways, with the makes it ideal for precision integrators and current best method depending on the temperature region to be sources. Figure 5 shows the LT1880 providing a simple emphasized and the particular ADC that will be reading precision current source for a remote 1kΩ RTD on a 4-wire the voltage. R5 100 180Ω, 5% C + (pF) 10 F F VOUT = 1.00V AT 0°C + 3.85mV/°C 1kΩ –50°C TO 600°C – AT 0°C RTD* RISE TIME C1 1 5V 0.1μF RISE TIME (μs), C R4 1k, 5% – R1 100mV OUTPUT STEP LT1880 0.1 1.24K + 0.1 1 10 100 1000 0.1% CD (pF) R2 1880 F04 10Ω R3 1% 150k, 1%
Figure 4. Feedback CF and Rise Time vs Photodiode CD
LT1634ACS8 -1.25 5V *OMEGA F3141 1kΩ, 0.1% PLATINUM RTD (800) 826-6342 1880 F05
Figure 5. Single Supply Current Source for Platinum RTD
1880fa 10
APPLICATIONS INFORMATION
The transimpedance gain is set to 51.1kΩ by RF. The connection. The LT1634 reference places 1.25V at the feedback capacitor, CF, may be as large as desired where noninverting input of the LT1880, which then maintains response time is not an issue, or it may be selected for its inverting input at the same voltage by driving 1mA maximally flat response and highest possible bandwidth of current through the RTD and the total 1.25kΩ of given a photodiode capacitance CD. Figure 4 shows a resistance set by R1 and R2. Imprecise components R4 chart of CF and rise time versus CD for maximally flat and C1 ensure circuit stability, which would otherwise be response. Total output offset is below 262μV, worst-case, excessively dependant on the cable characteristics. R5 is over temperature (0°C to 70°C). With a 5V output swing, also noncritical and is included to improve ESD immunity this guarantees a minimum 86dB dynamic range over and decouple any cable capacitance from the LT1880’s temperature (0°C to 70°C), and a full-scale photodiode output. The 4-wire cable allows Kelvin sensing of the RTD current of 98μA. voltage while excluding the cable IR drops from the voltage reading. With 1mA excitation, a 1kΩ RTD will have 1V
Single-Supply Current Source for Platinum RTD
across it at 0°C, and +3.85mV/°C temperature response. The precision, low bias current input stage of the LT1880 This voltage can be easily read in myriad ways, with the makes it ideal for precision integrators and current best method depending on the temperature region to be sources. Figure 5 shows the LT1880 providing a simple emphasized and the particular ADC that will be reading precision current source for a remote 1kΩ RTD on a 4-wire the voltage. R5 100 180Ω, 5% C + (pF) 10 F F VOUT = 1.00V AT 0°C + 3.85mV/°C 1kΩ –50°C TO 600°C – AT 0°C RTD* RISE TIME C1 1 5V 0.1μF RISE TIME (μs), C R4 1k, 5% – R1 100mV OUTPUT STEP LT1880 0.1 1.24K + 0.1 1 10 100 1000 0.1% CD (pF) R2 1880 F04 10Ω R3 1% 150k, 1%
Figure 4. Feedback CF and Rise Time vs Photodiode CD
LT1634ACS8 -1.25 5V *OMEGA F3141 1kΩ, 0.1% PLATINUM RTD (800) 826-6342 1880 F05
Figure 5. Single Supply Current Source for Platinum RTD
1880fa 10
