Datasheet LT1024 (Analog Devices) - 8

L T1 0 2 4
U U W U APPLICATIO S I FOR ATIO Achieving Picoampere/Microvolt Performance
In order to realize the picoampere/microvolt level Microvolt level error voltages can also be generated in the accuracy of the LT1024, proper care must be exercised. external circuitry. Thermocouple effects, caused by tem- For example, leakage currents in circuitry external to the perature gradients across dissimilar metals at the con- op amp can significantly degrade performance. High qual- tacts to the input terminals, can exceed the inherent drift ity insulation should be used (e.g., Teflon™, Kel-F); clean- of the amplifier. Air currents over device leads should be ing of all insulating surfaces to remove fluxes and other minimized, package leads should be short, and the two residues will probably be required. Surface coating may be input leads should be as close together as possible and necessary to provide a moisture barrier in high humidity maintained at the same temperature. environments. Board leakage can be minimized by encircling the input circuitry with a guard ring operated at a potential close to that of the inputs: in inverting configurations, the guard ring should be tied to ground; in noninverting connec- tions, to the inverting input. Guarding both sides of the printed circuit board is required. Bulk leakage reduction depends on the guard ring width. Nanoampere level leak- age into the offset trim terminals can affect offset voltage and drift with temperature. Teflon is a trademark of Dupont.
Test Circuit for Offset Voltage and its Drift with Temperature
R1 50k* 15V 14 (7) 3 – (10) R2 13 LT1024 V0 100Ω* 4 (6) + (11) RESISTORS MUST HA * VE LOW THERMOELECTRIC POTENTIAL R3 12 (5) 50k* THIS CIRCUIT IS ALSO USED AS THE BURN-IN ** –15V CONFIGURATION FOR THE LT1024. WITH SUPPLY VOLTAGES INCREASED TO ±20V, R1 = R3 = 20k, R2 = 200Ω, AV = 100 VO = 1000V0S LT1024 • AI02 1024fa 8