Datasheet LT1007, LT1037 (Analog Devices) - 9

LT1007/LT1037
U U W U APPLICATIONS INFORMATION General Offset Voltage and Drift
The LT1007/LT1037 series devices may be inserted Thermocouple effects, caused by temperature gradients directly into OP-07, OP-27, OP-37 and 5534 sockets with across dissimilar metals at the contacts to the input or without removal of external compensation or nulling terminals, can exceed the inherent drift of the amplifier components. In addition, the LT1007/LT1037 may be unless proper care is exercised. Air currents should be fitted to 741 sockets with the removal or modification of minimized, package leads should be short, the two input external nulling components. leads should be close together and maintained at the same temperature.
Offset Voltage Adjustment
The circuit shown to measure offset voltage is also used The input offset voltage of the LT1007/LT1037 and its drift as the burn-in configuration for the LT1007/LT1037, with with temperature, are permanently trimmed at wafer the supply voltages increased to ±20V (Figure 3). testing to a low level. However, if further adjustment of VOS is necessary, the use of a 10kΩ nulling potentiometer 50k* will not degrade drift with temperature. Trimming to a 15V value other than zero creates a drift of (VOS/ 300)µV/°C, e.g., if V 2 – OS is adjusted to 300µV, the change in drift will be 7 1µV/°C (Figure 1). LT1007 6 100Ω* VOUT LT1037 3 + The adjustment range with a 10kΩ pot is approximately VOUT = 1000VOS 4 ± *RESISTORS MUST HAVE LOW 2.5mV. If less adjustment range is needed, the sensitivity 50k* THERMOELECTRIC POTENTIAL –15V and resolution of the nulling can be improved by using a 1007/37 F03 smaller pot in conjunction with fixed resistors. The ex- ample has an approximate null range of ±200µV
Figure 3. Test Circuit for Offset Voltage and Offset Voltage Drift with Temperature
(Figure 2). 10k
Unity-Gain Buffer Application (LT1007 Only)
15V 1 When R 2 – 8 F ≤ 100Ω and the input is driven with a fast, large- 7 6 signal pulse (>1V), the output waveform will look as LT1007 INPUT OUTPUT LT1037 shown in the pulsed operation diagram (Figure 4). 3 + 4 During the fast feedthrough-like portion of the output, the –15V input protection diodes effectively short the output to the 1007/37 F01 input and a current, limited only by the output short-circuit
Figure 1. Standard Adjustment
protection, will be drawn by the signal generator. With RF ≥ 500Ω, the output is capable of handling the current 1k 15V requirements (IL ≤ 20mA at 10V) and the amplifier stays 4.7k in its active mode and a smooth transition will occur. 4.7k 1 RF 2 – 8 7 LT1007 6 – OUTPUT LT1037 3 + 2.8V/µs 4 OUTPUT + LT1007 –15V 1007/37 F02 1007/37 F04
Figure 2. Improved Sensitivity Adjustment Figure 4. Pulsed Operation
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