High Precision
±10 V Reference
AD688
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
FUNCTIONAL BLOCK DIAGRAM
NOISE
REDUCTION
7
V
HIGH
6
A3 IN
4
+10V OUT
SENSE
3
A3
1
R
B
A1
+10V OUT
FORCE
AD688
R4
A4
14
–10V OUT
R1
SENSE
R2
15
R5
–10V OUT
FORCE
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,
R3
A2
R6
2
+V
S
16
–V
S
5
9
10
8
12
11
13
00815-001
GAIN
ADJ
GND
SENSE
+IN
NC
V
LOW
BAL
ADJ
NC
A4 IN
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.
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.
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.
2.
3.
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
TABLE OF CONTENTS
Specifications..................................................................................... 3
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
Turn On Time................................................................................8
Temperature Performance............................................................9
Kelvin Connections.......................................................................9
Dynamic Performance............................................................... 11
Bridge Driver Circuit ................................................................. 12
Outline Dimensions ....................................................................... 13
Ordering Guide .......................................................................... 13
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
Rev. B | Page 2 of 16
AD688
SPECIFICATIONS
Typical @ 25°C, +10 V output, V
S
= ±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
Min
Typ
Max
OUTPUT VOLTAGE ERROR
+10 V,
−10
V Outputs
±10 V TRACKING ERROR
OUTPUT VOLTAGE DRIFT
+10 V, −10 V Outputs
0°C to +70°C (A, B)
−40°C to +85°C (A, B)
GAIN ADJ AND BAL ADJ
2
Trim Range
Input Resistance
LINE REGULATION
T
MIN
to T
MAX 3
LOAD REGULATION
T
MIN
to T
MAX
+10 V Output, 0<I
OUT
<10 mA
−10 V Output, −10<I
OUT
<0 mA
SUPPLY CURRENT
T
MIN
to T
MAX
Power Dissipation
OUTPUT NOISE (ANY OUTPUT)
0.1 Hz to 10 Hz
Spectral Density, 100 Hz
LONG-TERM STABILITY (@ 25°C)
BUFFER AMPLIFIERS
Offset Voltage
Offset Voltage Drift
Bias Current
Open-Loop Gain
Output Current A3, A4
Common-Mode Rejection (A3, A4)
V
CM
= 1 V p-p
Short-Circuit Current
TEMPERATURE RANGE
Specified Performance
A, B Grades
1
2
AD688BQ
Min
Typ Max
−2
−1.5
+2
+1.5
AD688ARWZ
Min
Typ
Max
−4
−1.5
+4
+1.5
Unit
mV
mV
−5
−3
+5
+3
±2
−3
±5
150
–200
+200
+3
–1.5
–3
±5
150
–200
+1.5
+3
–8
±5
150
+8
ppm/°C
ppm/°C
mV
kΩ
+200
–200
+200
µV/V
±50
±50
9
270
6
140
15
100
1
20
110
−10
100
50
+10
−10
100
50
12
360
9
270
6
140
15
100
1
20
110
±50
±50
12
360
6
140
15
100
1
20
110
+10
−10
100
50
±50
±50
12
360
µV/mA
µV/mA
mA
mW
µV p-p
nV√Hz
ppm/1000 hours
µV
µV/°C
nA
dB
mA
dB
mA
+10
−40
+85
−40
+85
−40
+85
°C
See Figure 4 for output configuration.
Gain and balance adjustments guaranteed capable of trimming output voltage error and symmetry error to zero.
3
Test Conditions: +V
S
= +18 V, −V
S
= –18 V; +V
S
= +13.5 V,
−V
S
= −13.5 V.
Rev. B | Page 3 of 16
AD688
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter
+V
S
to −V
S
Power Dissipation (25°C)
Q Package
Storage Temperature
Lead Temperature
(Soldering, 10 s)
Package Thermal Resistance
Q (θ
JA
/θ
JC
)
Output Protection:
All outputs safe if shorted
to ground
Rating
36 V
600 mW
−65°C to +150°C
+300°C
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.
120/35°C/W
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 degrada-
tion or loss of functionality.
Rev. B | Page 4 of 16
AD688
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
+10V OUT FORCE
1
+V
S 2
+10V OUT SENSE
3
A3 IN
4
16
15
–V
S
–10V OUT FORCE
–10V OUT SENSE
AD688
14
TOP VIEW
13
A4 IN
(Not to Scale)
12
BAL ADJ
GAIN ADJ
5
V
HIGH 6
NOISE REDUCTION
7
V
LOW 8
11
10
9
NC
NC
00815-002
GND SENSE +IN
NC = NO CONNECT
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Mnemonic
+10 V OUT FORCE
+V
S
+10 V OUT SENSE
A3 IN
GAIN ADJ
V
HIGH
NOISE REDUCTION
V
LOW
GND SENSE +IN
NC
NC
BAL ADJ
A4 IN
−10 V OUT SENSE
−10 V OUT FORCE
−V
S
Description
+10 V Output with Kelvin Force. Connect to Pin 3.
Positive Power Supply.
+10 V Output with Kelvin Sense. Connect to Pin 1.
+ Input to A3. Connect to V
HIGH
, Pin 6.
Reference Gain Adjustment for Calibration. See the Calibration section.
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.
Unbuffered Reference Low Output.
Gound with Kelvin Sense.
No Connection. Leave floating.
No Connection. Leave floating.
Reference Centering Adjustment for Calibration. See the Calibration section.
+ Input to A4. Connect to V
LOW
, Pin 8.
−10 V Output with Kelvin Sense. Connect to Pin 15.
−10 V Output with Kelvin Force. Connect to Pin 14.
Negative Power Supply.
Rev. B | Page 5 of 16
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