AD581
ABSOLUTE MAXIMUM RATINGS
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 V
Power Dissipation @ +25°C . . . . . . . . . . . . . . . . . . . . 600 mW
Operating Junction Temperature Range . . . . –55°C to +150°C
Lead Temperature (Soldering 10 sec) . . . . . . . . . . . . . +300°C
Thermal Resistance
Junction-to-Ambient . . . . . . . . . . . . . . . . . . . . . . . 150°C/W
APPLYING THE AD581
The AD581 is easy to use in virtually all precision reference
applications. The three terminals are simply primary supply,
ground, and output, with the case grounded. No external com-
ponents are required even for high precision applications; the
degree of desired absolute accuracy is achieved simply by select-
ing the required device grade. The AD581 requires less than
1 mA quiescent current from an operating supply range of
12 to 30 volts.
Figure 3. Simplified Schematic
VOLTAGE VARIATION VS. TEMPERATURE
Figure 1. AD581 Pin Configuration (Bottom View)
An external fine trim may be desired to set the output level to
exactly 10.000 volts within less than a millivolt (calibrated to a
main system reference). System calibration may also require a
reference slightly different from 10.00 volts. In either case, the
optional trim circuit shown in Figure 2 can offset the output by
up to
±
30 millivolts (with the 22
Ω
resistor), if needed, with
minimal effect on other device characteristics.
Some confusion exists in the area of defining and specifying
reference voltage error over temperature. Historically, references
have been characterized using a maximum deviation per degree
Centigrade; i.e., 10 ppm/°C. However, because of nonlinearities
in temperature characteristics, which originated in standard
Zener references (such as “S” type characteristics) most manu-
facturers have begun to use a maximum limit error band approach
to specify devices. This technique involves measurement of the
output at 3, 5 or more different temperatures to guarantee that
the output voltage will fall within the given error band. The
temperature characteristic of the AD581 consistently follows the
S-curve shown in Figure 4. Three-point measurement of each
device guarantees the error band over the specified temperature
range.
Figure 2. Optional Fine Trim Configuration
Figure 4. Typical Temperature Characteristic
The error band which is guaranteed with the AD581 is the
maximum deviation from the initial value at +25°C; this error
band is of more use to a designer than one which simply guaran-
tees the maximum total change over the entire range (i.e., in the
latter definition, all of the changes could occur in the positive
direction). Thus, with a given grade of the AD581, the designer
can easily determine the maximum total error from initial
tolerance plus temperature variation (e.g., for the AD581T,
REV. B
–3–
AD [ ANALOG DEVICES ]
