Datasheet LTZ1000, LTZ1000A (Analog Devices) - 4

LTZ1000/LTZ1000A
block DiagraM
1 8 3 5 * * Q2 Q1 * 2 6 4 7 *SUBSTRATE DEVICES–DO NOT FORWARD BIAS 1000 TA07
applicaTions inForMaTion
LTZ1000 and LTZ1000A are capable of providing ultimate should be connected to equal size PC traces to equalize voltage reference performance. Temperature drifts of better the heat loss and maintain them at similar temperatures. than 0.03ppm/°C and long-term stability on the order of The bottom portion of the PC board should be shielded 1µV per month can be achieved. Noise of about 0.15ppm against air currents as well. can also be obtained. This performance is at the expense Resistors, as well as having resistance temperature coef- of circuit complexity, since external influences can easily ficients, can generate thermocouple effects. Some types of cause output voltage shifts of more than 1ppm. resistors can generate hundreds of microvolts of thermo- Thermocouple effects are one of the worst problems and couple voltage. These thermocouple effects in the resistor can give apparent drifts of many ppm/°C as well as cause can also interfere with the output voltage. Wire wound low frequency noise. The kovar input leads of the TO-5 resistors usually have the lowest thermocouple voltage, package form thermocouples when connected to copper while tin oxide type resistors have very high thermocouple PC boards. These thermocouples generate outputs of voltage. Film resistors, especially Vishay precision film 35µV/°C. It is mandatory to keep the zener and transistor resistors, can have low thermocouple voltage. leads at the same temperature, otherwise 1ppm to 5ppm Ordinary breadboarding techniques are not good enough shifts in the output voltage can easily be expected from to give stable output voltage with the LTZ1000 family these thermocouples. devices. For breadboarding, it is suggested that a small Air currents blowing across the leads can also cause small printed circuit board be made up using the reference, the temperature variations, especially since the package is amplifier and wire wound resistors. Care must be taken to heated. This will look like 1ppm to 5ppm of low frequency ensure that heater current does not flow through the same noise occurring over a several minute period. For best ground lead as the negative side of the reference (emitter results, the device should be located in an enclosed area of Q1). Current changes in the heater could add to, or and well shielded from air currents. subtract from, the reference voltage causing errors with Certainly, any temperature gradient externally generated, temperature. Single point grounding using low resistance say from a power supply, should not appear across the wiring is suggested. critical circuitry. The leads to the transistor and zener 1000afe 4 For more information www.linear.com/LTZ1000 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Revision History Package Description Related Parts