ANALOG DEVICES AD688 Service Manual
High Precision
www.BDTIC.com/ADI
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.
±10 V Reference
FUNCTIONAL BLOCK DIAGRAM
NOISE
REDUCTION
7 6 4 3
R
B
R2
R3
A2
5 9 10 8 12 11 13
GND
GAIN
SENSE
ADJ
+IN
V
HIGH
A1
R1
NC
V
LOW
NC = NO CONNECT
R4
R5
Figure 1.
A3 IN
BAL
ADJ
+10V OUT
AD688
R6
NC
SENSE
A4 IN
AD688
A3
A4
+10V OUT
1
FORCE
–10V OUT
14
SENSE
–10V OUT
15
FORCE
+V
2
16
–V
S
S
00815-001
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
o
the −40
C to +85oC temperature range, the AD688 is offered in
wide body 16-lead SOIC and 16-lead CERDIP packages,
Covered by Patent Number 4,644,253
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 finetrim 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.
Rev. B
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 © 2005 Analog Devices, Inc. All rights reserved.
AD688
www.BDTIC.com/ADI
TABLE OF CONTENTS
Specifications..................................................................................... 3
Turn On Ti me ................................................................................8
Absolute Maximum Ratings............................................................ 4
ESD Caution.................................................................................. 4
Pin Configuration and Function Descriptions............................. 5
Theory of Operation ........................................................................ 6
Applications....................................................................................... 7
Calibration..................................................................................... 7
Noise Performance and Reduction ............................................ 8
REVISION HISTORY
3/05—Rev. A to Rev. B
Updated Format..................................................................Universal
Added AD688ARWZ.........................................................Universal
Removed AD688SQ ...........................................................Universal
Updated Outline Dimensions....................................................... 13
Changes to Ordering Guide.......................................................... 13
Temperature Performance............................................................9
Kelvin Connections.......................................................................9
Dynamic Performance............................................................... 11
Bridge Driver Circuit ................................................................. 12
Outline Dimensions....................................................................... 13
Ordering Guide .......................................................................... 13
Rev. B | Page 2 of 16
AD688
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SPECIFICATIONS
Typical @ 25°C, +10 V output, VS = ±15 V unless otherwise noted.1 Specifications shown in boldface are tested on all production units at
final electrical test. Results from those tests are used to calculate outgoing quality levels. All min and max specifications are guaranteed.
Table 1.
AD688AQ AD688BQ AD688ARWZ
Min Typ Max Min Typ Max Min Typ Max Unit
OUTPUT VOLTAGE ERROR
+10 V, −10 V Outputs −5 +5 −2 +2 −4 +4
±10 V TRACKING ERROR
−3 +3 −1.5 +1.5 −1.5 +1.5
OUTPUT VOLTAGE DRIFT
+10 V, −10 V Outputs
0°C to +70°C (A, B) ±2
−40°C to +85°C (A, B)
−3 +3 –3 +3 –8
–1.5 +1.5
ppm/°C
+8
GAIN ADJ AND BAL ADJ2
Trim Range ± 5 ±5 ±5 mV
Input Resistance 150 150 150 kΩ
LINE REGULATION
to T
MAX
3
–200 +200 –200 +200 –200 +200
T
MIN
LOAD REGULATION
T
to T
MIN
MAX
+10 V Output, 0<I
−10 V Output, −10<I
<10 mA ±50 ±50 ±50 µV/mA
OUT
<0 mA ±50 ±50 ±50 µV/mA
OUT
SUPPLY CURRENT
T
to T
MIN
9
MAX
12
9
12
12
Power Dissipation 270 360 270 360 360 mW
OUTPUT NOISE (ANY OUTPUT)
0.1 Hz to 10 Hz 6 6 6 µV p-p
Spectral Density, 100 Hz 140 140 140 nV√Hz
LONG-TERM STABILITY (@ 25°C) 15 15 15 ppm/1000 hours
BUFFER AMPLIFIERS
Offset Voltage 100 100 100 µV
Offset Voltage Drift 1 1 1 µV/°C
Bias Current 20 20 20 nA
Open-Loop Gain 110 110 110 dB
Output Current A3, A4
−10 +10 −10 +10 −10 +10
Common-Mode Rejection (A3, A4)
VCM = 1 V p-p 100 100 100 dB
Short-Circuit Current 50 50 50 mA
TEMPERATURE RANGE
Specified Performance
A, B Grades −40 +85 −40 +85 −40 +85 °C
1
See for output configuration. Figure 4
2
Gain and balance adjustments guaranteed capable of trimming output voltage error and symmetry error to zero.
3
Test Conditions: +VS = +18 V, −VS = –18 V; +VS = +13.5 V, −VS = −13.5 V.
mV
mV
ppm/°C
µV/V
mA
mA
Rev. B | Page 3 of 16
AD688
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ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
+VS to −V
Power Dissipation (25°C)
Storage Temperature −65°C to +150°C
Lead Temperature
(Soldering, 10 s)
Package Thermal Resistance
Output Protection:
S
Q Package 600 mW
Q (θJA/θJC) 120/35°C/W
All outputs safe if shorted
to ground
36 V
+300°C
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Stresses above those listed under “Absolute Maximum Ratings”
may cause permanent damage to the device. This is a stress
rating only and functional operation of the device at these or
any other conditions above those indicated in the operational
sections of this specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may
affect reliability.
Rev. B | Page 4 of 16
AD688
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PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
+10V OUT FORCE
+10V OUT SENSE
GAIN ADJ
NOISE REDUCTION
1
+V
2
S
3
A3 IN
4
5
V
6
HIGH
7
V
8
LOW
NC = NO CONNECT
AD688
TOP VIEW
(Not to Scale)
–V
16
S
–10V OUT FORCE
15
14
–10V OUT SENSE
A4 IN
13
BAL ADJ
12
NC
11
10
NC
GND SENSE +IN
9
00815-002
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description
1 +10 V OUT FORCE +10 V Output with Kelvin Force. Connect to Pin 3.
2 +V
S
Positive Power Supply.
3 +10 V OUT SENSE +10 V Output with Kelvin Sense. Connect to Pin 1.
4 A3 IN + Input to A3. Connect to V
HIGH
, Pin 6.
5 GAIN ADJ Reference Gain Adjustment for Calibration. See the Calibration section.
6 V
HIGH
7 NOISE REDUCTION
Unbuffered Reference High Output.
Noise Filtering Pin. Connect external 1 µF capacitor to ground to reduce output noise, see the
Noise Performance and Reduction section. May be left open.
8 V
LOW
Unbuffered Reference Low Output.
9 GND SENSE +IN Gound with Kelvin Sense.
10 NC No Connection. Leave floating.
11 NC No Connection. Leave floating.
12 BAL ADJ Reference Centering Adjustment for Calibration. See the Calibration section.
13 A4 IN + Input to A4. Connect to V
LOW
, Pin 8.
14 −10 V OUT SENSE −10 V Output with Kelvin Sense. Connect to Pin 15.
15 −10 V OUT FORCE −10 V Output with Kelvin Force. Connect to Pin 14.
16 −V
S
Negative Power Supply.
Rev. B | Page 5 of 16
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