Datasheet AD587 (Analog Devices) - 6

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AD587 THEORY OF OPERATION
The AD587 consists of a proprietary buried Zener diode
NOISE PERFORMANCE AND REDUCTION
reference, an amplifier to buffer the output, and several high Noise generated by the AD587 is typically less than 4 μV p-p stability thin-film resistors, as shown in Figure 3. This design over the 0.1 Hz to 10 Hz band. Noise in a 1 MHz bandwidth is results in a high precision monolithic 10 V output reference approximately 200 μV p-p. The dominant source of this noise is with initial offset of 5 mV or less. The temperature-compensa- the buried Zener, contributing approximately 100 nV/√Hz. By tion circuitry provides the device with a temperature coefficient comparison, the contribution of the op amp is negligible. of less than 5 ppm/°C. Figure 5 shows the 0.1 Hz to 10 Hz noise of a typical AD587.
NOISE +V
The noise measurement is made with a band-pass filter made
IN REDUCTION 2 8
of a 1-pole high-pass filter with a corner frequency at 0.1 Hz
R
and a 2-pole low-pass filter with a corner frequency at 12.6 Hz
S
to create a filter with a 9.922 Hz bandwidth.
A1 6 VOUT RF 1µV 5s RT 5 TRIM 100 90 RI AD587 4 1µV GND
3
NOTE
00
PIN 1, PIN 3, AND PIN 7 ARE INTERNAL TEST
0-
POINTS. NO CONNECTIONS TO THESE POINTS.
53 00 Figure 3. Functional Block Diagram
10 0%
A capacitor can be added at the NOISE REDUCTION pin 05 -0 (Pin 8) to form a low-pass filter with RS to reduce the noise 30 05 0 contribution of the Zener to the circuit. Figure 5. 0.1 Hz to 10 Hz Noise
APPLYING THE AD587
If further noise reduction is desired, an external capacitor can The AD587 is simple to use in virtually all precision reference be added between the NOISE REDUCTION pin and ground, applications. When power is applied to Pin 2 and Pin 4 is as shown in Figure 4. This capacitor, combined with the 4 kΩ RS grounded, Pin 6 provides a 10 V output. No external compo- and the Zener resistances, forms a low-pass filter on the output nents are required; the degree of desired absolute accuracy is of the Zener cell. A 1 μF capacitor has a 3 dB point at 40 Hz achieved simply by selecting the required device grade. The and reduces the high frequency (up to 1 MHz) noise to about AD587 requires less than 4 mA quiescent current from an 160 μV p-p. Figure 6 shows the 1 MHz noise of a typical AD587, operating supply of 15 V. both with and without a 1 μF capacitor. Fine trimming may be desired to set the output level to exactly
200µV 50µs
10.000 V (calibrated to a main system reference). System cali- bration may also require a reference voltage that is slightly
100 90
different from 10.000 V, for example, 10.24 V for binary
CN – 1µF
applications. In either case, the optional fine-trimming circuit shown in Figure 4 can offset the output by as much as 300 mV with minimal effect on other device characteristics.
+VIN NO CN 10 0% 2 OPTIONAL NOISE- V
6
IN REDUCTION
-00 0
CAPACITOR V
53
OUT 6 OUTPUT 8 NOISE
00
REDUCTION
Figure 6. Effect of 1 μF Noise-Reduction Capacitor on Broadband Noise
AD587 CN TRIM 5 10kΩ 1µF GND 4
4 00 0- 53 00 Figure 4. Optional Fine-Trimming Configuration Rev. H | Page 6 of 12 Document Outline FEATURES FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS THEORY OF OPERATION APPLYING THE AD587 NOISE PERFORMANCE AND REDUCTION TURN-ON TIME DYNAMIC PERFORMANCE LOAD REGULATION TEMPERATURE PERFORMANCE NEGATIVE REFERENCE VOLTAGE FROM AN AD587 APPLICATIONS INFORMATION USING THE AD587 WITH CONVERTERS 10 V Reference with Multiplying CMOS DACs or ADCs Precision Current Source Precision High Current Supply OUTLINE DIMENSIONS ORDERING GUIDE