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
the −40
o
C to +85
o
C temperature range, the AD688 is offered in
wide body 16-lead SOIC and 16-lead CERDIP packages,
FUNCTIONAL BLOCK DIAGRAM
R3
R
B
R1
R2
R4
R5
R6
GAIN
ADJ
GND
SENSE
+IN
NC
V
LOW
BAL
ADJ
NC
A4 IN
–V
S
+V
S
–10V OUT
FORCE
–10V OUT
SENSE
+10V OUT
FORCE
+10V OUT
SENSE
A3 IN
V
HIGH
NOISE
REDUCTION
A1
A4
A3
A2
AD688
7 6 4 3
1
14
2
15
16
5 9 10 8 12 11 13
00815-001
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.
