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LTZ1000 Datasheet(PDF) 4 Page - Linear Technology |
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LTZ1000 Datasheet(HTML) 4 Page - Linear Technology |
4 / 8 page LTZ1000/LTZ1000A 4 1000afd applicaTions inForMaTion LTZ1000 and LTZ1000A are capable of providing ultimate voltagereferenceperformance.Temperaturedriftsofbetter than 0.03ppm/°C and long-term stability on the order of 1µV per month can be achieved. Noise of about 0.15ppm can also be obtained. This performance is at the expense of circuit complexity, since external influences can easily cause output voltage shifts of more than 1ppm. Thermocouple effects are one of the worst problems and can give apparent drifts of many ppm/°C as well as cause low frequency noise. The kovar input leads of the TO-5 package form thermocouples when connected to copper PC boards. These thermocouples generate outputs of 35µV/°C. It is mandatory to keep the zener and transistor leads at the same temperature, otherwise 1ppm to 5ppm shifts in the output voltage can easily be expected from these thermocouples. Air currents blowing across the leads can also cause small temperature variations, especially since the package is heated. This will look like 1ppm to 5ppm of low frequency noise occurring over a several minute period. For best results, the device should be located in an enclosed area and well shielded from air currents. Certainly, any temperature gradient externally generated, say from a power supply, should not appear across the critical circuitry. The leads to the transistor and zener should be connected to equal size PC traces to equalize the heat loss and maintain them at similar temperatures. The bottom portion of the PC board should be shielded against air currents as well. Resistors, as well as having resistance temperature coef- ficients,cangeneratethermocoupleeffects.Sometypesof resistors can generate hundreds of microvolts of thermo- couple voltage. These thermocouple effects in the resistor can also interfere with the output voltage. Wire wound resistors usually have the lowest thermocouple voltage, while tin oxide type resistors have very high thermocouple voltage. Film resistors, especially Vishay precision film resistors, can have low thermocouple voltage. Ordinary breadboarding techniques are not good enough to give stable output voltage with the LTZ1000 family devices. For breadboarding, it is suggested that a small printed circuit board be made up using the reference, the amplifier and wire wound resistors. Care must be taken to ensure that heater current does not flow through the same ground lead as the negative side of the reference (emitter of Q1). Current changes in the heater could add to, or subtract from, the reference voltage causing errors with temperature. Single point grounding using low resistance wiring is suggested. block DiagraM 1 8 Q2 Q1 3 5 6 2 4 7 * * *SUBSTRATE DEVICES–DO NOT FORWARD BIAS 1000 TA07 |
Similar Part No. - LTZ1000_12 |
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Similar Description - LTZ1000_12 |
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