Datasheet LTC1052, LTC7652 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Zero-Drift Operational Amplifier |
| Pages / Page | 24 / 9 — APPLICATIO S I FOR ATIO. Microvolts. Figure 2. Table 1. Resistor Thermal … |
| File Format / Size | PDF / 871 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Microvolts. Figure 2. Table 1. Resistor Thermal EMF. RESISTOR TYPE. THERMAL EMF/. C GRADIENT
Model Line for this Datasheet
Text Version of Document
LTC1052/LTC7652
U U W U APPLICATIO S I FOR ATIO
connections, to the inverting input. Guarding both sides Figure 2 is an example of the introduction of an of the printed circuit board is required. Bulk leakage unnecessary resistor to promote differential thermal reduction depends on the guard ring width. balance. Maintaining compensating junctions in close physical proximity will keep them at the same temperature and reduce thermal EMF errors. NOMINALLY UNNECESSARY RESISTOR USED TO THERMALLY BALANCE OTHER LEAD WIRE/SOLDER/COPPER INPUT RESISTOR TRACE JUNCTION + LTC1052 OUTPUT – RESISTOR LEAD, SOLDER, COPPER TRACE JUNCTION
Microvolts
Thermocouple effects must be considered if the LTC1052’s LTC1052/7652 • AI03 ultralow drift is to be fully utilized. Any connection
Figure 2
of dissimilar metals forms a thermoelectric junction producing an electric potential which varies with When connectors, switches, relays and/or sockets are temperature (Seebeck effect). As temperature sensors, necessary they should be selected for low thermal EMF thermocouples exploit this phenomenon to produce activity. The same techniques of thermally balancing and useful information. In low drift amplifier circuits the effect coupling the matching junctions are effective in reducing is a primary source of error. the thermal EMF errors of these components. Connectors, switches, relay contacts, sockets, resistors, Resistors are another source of thermal EMF errors. solder, and even copper wire are all candidates for Table 1 shows the thermal EMF generated for different thermal EMF generation. Junctions of copper wire from resistors. The temperature gradient across the resistor is different manufacturers can generate thermal EMFs of important, not the ambient temperature. There are two 200nV/°C—4 times the maximum drift specification of junctions formed at each end of the resistor and if these the LTC1052. The copper/kovar junction, formed when junctions are at the same temperature, their thermal EMFs wire or printed circuit traces contact a package lead, has will cancel each other. The thermal EMF numbers are a thermal EMF of approximately 35µV/°C–700 times the approximate and vary with resistor value. High values give maximum drift specification of the LTC1052. higher thermal EMF. Minimizing thermal EMF-induced errors is possible if judicious attention is given to circuit board layout and
Table 1. Resistor Thermal EMF
component selection. It is good practice to minimize the
RESISTOR TYPE THERMAL EMF/
°
C GRADIENT
number of junctions in the amplifier’s input signal path. Tin Oxide ~mV/’C Avoid connectors, sockets, switches and relays where Carbon Composition ~450µV/°C possible. In instances where this is not possible, attempt Metal Film ~20µV/°C to balance the number and type of junctions so that Wire Wound differential cancellation occurs. Doing this may involve Evenohm ~2µV/°C deliberately introducing junctions to offset unavoidable Manganin ~2µV/°C junctions. 1052fa 9
U U W U APPLICATIO S I FOR ATIO
connections, to the inverting input. Guarding both sides Figure 2 is an example of the introduction of an of the printed circuit board is required. Bulk leakage unnecessary resistor to promote differential thermal reduction depends on the guard ring width. balance. Maintaining compensating junctions in close physical proximity will keep them at the same temperature and reduce thermal EMF errors. NOMINALLY UNNECESSARY RESISTOR USED TO THERMALLY BALANCE OTHER LEAD WIRE/SOLDER/COPPER INPUT RESISTOR TRACE JUNCTION + LTC1052 OUTPUT – RESISTOR LEAD, SOLDER, COPPER TRACE JUNCTION
Microvolts
Thermocouple effects must be considered if the LTC1052’s LTC1052/7652 • AI03 ultralow drift is to be fully utilized. Any connection
Figure 2
of dissimilar metals forms a thermoelectric junction producing an electric potential which varies with When connectors, switches, relays and/or sockets are temperature (Seebeck effect). As temperature sensors, necessary they should be selected for low thermal EMF thermocouples exploit this phenomenon to produce activity. The same techniques of thermally balancing and useful information. In low drift amplifier circuits the effect coupling the matching junctions are effective in reducing is a primary source of error. the thermal EMF errors of these components. Connectors, switches, relay contacts, sockets, resistors, Resistors are another source of thermal EMF errors. solder, and even copper wire are all candidates for Table 1 shows the thermal EMF generated for different thermal EMF generation. Junctions of copper wire from resistors. The temperature gradient across the resistor is different manufacturers can generate thermal EMFs of important, not the ambient temperature. There are two 200nV/°C—4 times the maximum drift specification of junctions formed at each end of the resistor and if these the LTC1052. The copper/kovar junction, formed when junctions are at the same temperature, their thermal EMFs wire or printed circuit traces contact a package lead, has will cancel each other. The thermal EMF numbers are a thermal EMF of approximately 35µV/°C–700 times the approximate and vary with resistor value. High values give maximum drift specification of the LTC1052. higher thermal EMF. Minimizing thermal EMF-induced errors is possible if judicious attention is given to circuit board layout and
Table 1. Resistor Thermal EMF
component selection. It is good practice to minimize the
RESISTOR TYPE THERMAL EMF/
°
C GRADIENT
number of junctions in the amplifier’s input signal path. Tin Oxide ~mV/’C Avoid connectors, sockets, switches and relays where Carbon Composition ~450µV/°C possible. In instances where this is not possible, attempt Metal Film ~20µV/°C to balance the number and type of junctions so that Wire Wound differential cancellation occurs. Doing this may involve Evenohm ~2µV/°C deliberately introducing junctions to offset unavoidable Manganin ~2µV/°C junctions. 1052fa 9
