REV. 0

ADR512

–5–

Adjustable Precision Voltage Source

The ADR512, combined with a precision low input bias op amp

such as the AD8610, can be used to output a precise adjustable

voltage. Figure 2 illustrates the implementation of this application

using the ADR512.

circuit, which is completely dependent on resistors R2 and R1.

V

R

R

OUT

=+

1

2

1

(4)

An additional capacitor in parallel with R2 can be added to filter

out high frequency noise. The value of C2 is dependent on the

value of R2.

R1

R2

AD8610

ADR512

1.2V

C2 (OPTIONAL)

Figure 2. Adjustable Precision Voltage Source

Output Voltage Trim

Using a mechanical or digital potentiometer, the output voltage

of the ADR512 can be trimmed

±0.5%. The circuit in Figure 3

illustrates how the output voltage can be trimmed, using a 10 k

Ω

potentiometer.

R1

100k

POT

50k

ADR512

Figure 3. Output Voltage Trim

Using the ADR512 with Precision Data Converters

The compact ADR512 package and the device’s low minimum

operating current requirement make it ideal for use in battery-

powered portable instruments, such as the AD7533 CMOS

multiplying DAC, that use precision data converters.

Figure 4 shows the ADR512 serving as an external reference to

the AD7533, a CMOS multiplying DAC. Such a DAC requires

a negative voltage input in order to provide a positive output

range. In this application, the ADR512 is supplying a –1.2 V

reference to the REF input of the AD7533.

MSB

LSB

1

2

3

1

1

15

09

R2

ADR512

AD7533

Figure 4. ADR512 as a Reference for a 10-Bit

CMOS DAC (AD7533)

Precise Negative Voltage Reference

The ADR512 is suitable for use in applications where a precise

negative voltage reference is desired, including the application

detailed in Figure 4.

Figure 5 shows the ADR512 configured to provide a –1.2 V output.

–1.2V

–

R1

ADR512

Figure 5. Precise –1.2 V Reference Configuration

Since the ADR512 characteristics resemble those of a Zener diode,

the cathode shown in Figure 5 will be 1.2 V higher with respect

to the anode (V+ with respect to V– on the ADR512 package).

Since the cathode of the ADR512 is tied to ground, the anode

must be –1.2 V.

R1 in Figure 5 should be chosen so that 100

µA to 10 mA is

provided to properly bias the ADR512.

R

V

I

DD

1

=

(5)

The resistor R1 should be chosen so that power dissipation is at

a minimum. An ideal resistor value can be determined through

manipulation of Equation 5.