Datasheet LT1236LS8 (Analog Devices) - 8

LT1236LS8
applicaTions inForMaTion
use a star-ground method, with the LT1236LS8 ground
Series Mode with Boost Transistor
tied directly to the load, rather than through a ground INPUT plane or other shared ground trace. This last method will R1 220Ω reduce drop in the ground trace between the LT1236LS8 2N3906 and the load. The ground wire in this case will carry only IN approximately 1mA, which is the ground current of the LT1236LS8 LT1236LS8, while the load return current will shunt to the OUT system ground separate from the reference-to-load path. GND LOAD R2* The following circuits show proper hook-up to minimize errors due to ground loops and line losses. Losses in the GROUND RETURN output lead can be greatly reduced by adding a PNP boost transistor if load currents are 5mA or higher. R2 can be *OPTIONAL—REDUCES CURRENT IN OUTPUT SENSE LEAD: R2 = 2.4k 1236ls8 AI04 added to further reduce current in the output sense lead.
Long-Term Drift Effects of Air Movement on Low Frequency Noise
Long-term drift cannot be extrapolated from accelerated The LT1236LS8 has very low noise because of the buried high temperature testing. This erroneous technique gives zener used in its design. In the 0.1Hz to 10Hz band, peak- drift numbers that are wildly optimistic. The only way to-peak noise is about 0.5ppm of the DC output. To achieve long-term drift can be determined is to measure it over this low noise, however, care must be taken to shield the the time interval of interest. reference from ambient air turbulence. Air movement can create noise because of thermoelectric differences between The LT1236LS8 long-term drift data was collected on 80 IC package leads and printed circuit board materials and/or parts that were soldered into printed circuit boards similar sockets. Power dissipation in the reference, even though it to a real world application. The boards were then placed rarely exceeds 20mW, is enough to cause small tempera- into a constant temperature oven with a TA = 35°C, their ture gradients in the package leads. Variations in thermal outputs were scanned regularly and measured with an 8.5 resistance, caused by uneven air flow, create differential digit DVM. Typical long-term drift is illustrated in Figure 1. lead temperatures, thereby causing thermoelectric voltage noise at the output of the reference. 200 NORMALIZED TO 10 HOURS 160 DUE TO SYSTEM WARM-UP
Standard Series Mode
120 80 LT1236LS8 40 KEEP THIS LINE RESISTANCE LOW INPUT IN OUT PPM 0 GND + –40 LOAD –80 –120 GROUND –160 RETURN 1236ls8 AI03 –200 0 500 1000 1500 2000 HOURS 1236ls8 F01
Figure 1. Long-Term Drift
1236ls8f 8 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 Package Description Typical Application Related Parts