AD584

REV. A

–4–

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.

Figure 2. Output Trimming

Figure 3. Schematic Diagram

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

Pin Programming

7.5 V

Join the 2.5 V and 5.0 V pins (2) and (3)

5.0 V

Connect the 5.0 V pin (2) to the output pin (1).

2.5 V

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 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 k

Ω, the upper limit of the output