High Precision

±10 V Reference

AD688

Rev. B

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FEATURES

±10 V tracking outputs

Kelvin connections

Low tracking error: 1.5 mV

Low initial error: 2.0 mV

Low drift: 1.5 ppm/°C

Low noise: 6 μV p-p

Flexible output force and sense terminals

High impedance ground sense

Wide body SOIC and CERDIP packages

GENERAL DESCRIPTION

The AD688 is a high precision ±10 V tracking reference. Low

tracking error, low initial error, and low temperature drift give

the AD688 reference absolute ±10 V accuracy performance

previously unavailable in monolithic form. The AD688 uses a

proprietary ion-implanted buried Zener diode, and laser wafer

drift trimming of high stability thin-film resistors to provide

outstanding performance.

The AD688 includes the basic reference cell and three

additional amplifiers. The amplifiers are laser-trimmed for low

offset and low drift and maintain the accuracy of the reference.

The amplifiers are configured to allow Kelvin connections to

the load and/or boosters for driving long lines or high current

loads, delivering the full accuracy of the AD688 where it is

required in the application circuit.

The low initial error allows the AD688 to be used as a system

reference in precision measurement applications requiring

12-bit absolute accuracy. In such systems, the AD688 can

provide a known voltage for system calibration; the cost of

periodic recalibration can therefore be eliminated.

Furthermore, the mechanical instability of a trimming

potentiometer and the potential for improper calibration can be

eliminated by using the AD688 and calibration software.

The AD688 is available in commercial version. Specified over

wide body 16-lead SOIC and 16-lead CERDIP packages,

FUNCTIONAL BLOCK DIAGRAM

R3

R1

R2

R4

R5

R6

GAIN

ADJ

GND

SENSE

+IN

NC

ADJ

NC

A4 IN

–10V OUT

FORCE

–10V OUT

SENSE

+10V OUT

FORCE

+10V OUT

SENSE

A3 IN

NOISE

REDUCTION

A1

A4

A3

A2

AD688

7

6

4

3

1

14

2

15

16

5

9

10

8

12

11

13

NC = NO CONNECT

Figure 1.

PRODUCT HIGHLIGHTS

1.

Precision Tracking. The AD688 offers precision tracking

±10 V Kelvin output connections with no external

components. Tracking error is less than 1.5 mV and fine-

trim is available for applications requiring exact symmetry

between the +10 V and −10 V outputs.

2.

Accuracy. The AD688 offers 12-bit absolute accuracy

without any user adjustments. Optional fine-trim

connections are provided for applications requiring higher

precision. The fine-trimming does not alter the operating

conditions of the Zener or the buffer amplifiers and thus

does not increase the temperature drift.

3.

Low output noise. Output noise of the AD688 is low—

typically 6 μV p-p. A pin is provided for broadband noise

filtering using an external capacitor.