AD584
APPLYING THE AD584
With power applied to Pins 8 and 4 and all other pins open, the
AD584 will produce a buffered nominal 10.0 V output between
Pins 1 and 4 (see Figure 1). The stabilized output voltage may
be reduced to 7.5 V, 5.0 V or 2.5 V by connecting the program-
ming pins as follows:
Output
Voltage
7.5 V
5.0 V
2.5 V
range will be about 20 V even for large values of R1. R2 should
not be omitted; its value should be chosen to limit the output to
a value which can be tolerated by the load circuits. If R2 is zero,
adjusting R1 to its lower limit will result in a loss of control over
the output voltage. If precision voltages are required to be set at
levels other than the standard outputs, the 20% absolute toler-
ance in the internal resistor ladder must be accounted for.
Alternatively, the output voltage can be raised by loading the
2.5 V tap with R3 alone. The output voltage can be lowered by
connecting R4 alone. Either of these resistors can be a fixed
resistor selected by test or an adjustable resistor. In all cases the
resistors should have a low temperature coefficient to match the
AD584 internal resistors, which have a negative T.C. less than
60 ppm/°C. If both R3 and R4 are used, these resistors should
have matched temperature coefficients.
When only small adjustments or trims are required, the circuit
of Figure 2 offers better resolution over a limited trim range.
The circuit can be programmed to 5.0 V, 7.5 V or 10 V and ad-
justed by means of R1 over a range of about
±
200 mV. To trim
the 2.5 V output option, R2 (Figure 2) can be reconnected to
the bandgap reference (Pin 6). In this configuration, the adjust-
ment should be limited to
±
100 mV in order to avoid affecting
the performance of the AD584.
Pin Programming
Join the 2.5 V and 5.0 V pins (2) and (3)
Connect the 5.0 V pin (2) to the output pin (1).
Connect the 2.5 V pin (3) to the output pin (1).
The options shown above are available without the use of any
additional components. Multiple outputs using only one
AD584, are also possible by simply buffering each voltage pro-
gramming pin with a unity-gain noninverting op amp.
Figure 2. Output Trimming
Figure 1. Variable Output Options
The AD584 can also be programmed over a wide range of out-
put voltages, including voltages greater than 10 V, by the ad-
dition of one or more external resistors. Figure 1 illustrates the
general adjustment procedure, with approximate values given
for the internal resistors of the AD584. The AD584 may be
modeled as an op amp with a noninverting feedback connection,
driven by a high stability 1.215 volt bandgap reference (see Fig-
ure 3 for schematic).
When the feedback ratio is adjusted with external resistors, the
output amplifier can be made to multiply the reference voltage
by almost any convenient amount, making popular outputs of
10.24 V, 5.12 V, 2.56 V or 6.3 V easy to obtain. The most
general adjustment (which gives the greatest range and poorest
resolution) uses R1 and R2 alone (see Figure 1). As R1 is ad-
justed to its upper limit the 2.5 V Pin 3 will be connected to the
output, which will reduce to 2.5 V. As R1 is adjusted to its
lower limit, the output voltage will rise to a value limited by R2.
For example, if R2 is about 6 kΩ, the upper limit of the output
Figure 3. Schematic Diagram
–4–
REV. A
AD [ ANALOG DEVICES ]
