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AD588 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD588
Beschreibung High Precision Voltage Reference
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
AD588 Datasheet, Funktion
High Precision Voltage Reference
AD588*
FEATURES
Low Drift: 1.5 ppm/؇C
Low Initial Error: 1 mV
Pin Programmable Output:
+10 V, +5 V, +65 V Tracking, –5 V, –10 V
Flexible Output Force and Sense Terminals
High Impedance Ground Sense
Machine lnsertable DIP Packaging
MIL-STD-883 Compliant Versions Available
GENERAL DESCRIPTION
The AD588 represents a major advance in the state-of-the-art
in monolithic voltage references. Low initial error and low tem-
perature drift give the AD588 absolute accuracy performance
previously not available in monolithic form. The AD588 uses a
proprietary ion-implanted buried Zener diode, and laser-wafer-
drift trimming of high stability thin-film resistors to provide
outstanding performance at low cost.
The AD588 includes the basic reference cell and three additional
amplifiers that provide pin programmable output ranges. The
amplifiers are laser-trimmed for low offset and low drift to main-
tain the accuracy of the reference. The amplifiers are configured
to allow Kelvin connections to the load and/or boosters for driv-
ing long lines or high current loads, delivering the full accuracy
of the AD588 where it is required in the application circuit.
The low initial error allows the AD588 to be used as a system
reference in precision measurement applications requiring 12-bit
absolute accuracy. In such systems, the AD588 can provide a
known voltage for system calibration in software, and the low
drift allows compensation for the drift of other components in
a system. Manual system calibration and 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 AD588 in conjunction with autocalibration software.
The AD588 is available in four versions. The AD588JQ and
AD588KQ and grades are packaged in a 16-lead CERDIP and
are specified for 0°C to 70°C operation. AD588AQ and BQ
grades are packaged in a 16-lead CERDIP and are specified for
the –25°C to +85°C industrial temperature range.
FUNCTIONAL BLOCK DIAGRAM
NOISE
REDUCTION
A3 OUT
VHIGH A3 IN SENSE
RB
A1
R1
R2
R3
A2
R4
R5
R6
A3
A3 OUT
FORCE
A4 OUT
SENSE
A4
A4 OUT
FORCE
AD588
+VS
–VS
GAIN GND GND
ADJ SENSE SENSE
+IN –IN
VLOW BAL VCT A4 IN
ADJ
PRODUCT HIGHLIGHTS
1. The AD588 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.
2. Output noise of the AD588 is very low—typically 6 µV p-p.
A pin is provided for additional noise filtering using an exter-
nal capacitor.
3. A precision ± 5 V tracking mode with Kelvin output connec-
tions is available with no external components. Tracking error
is less than 1 mV and a fine-trim is available for applications
requiring exact symmetry between the +5 V and –5 V outputs.
4. Pin strapping capability allows configuration of a wide vari-
ety of outputs: ± 5 V, +5 V, +10 V, –5 V, and –10 V dual
outputs or +5 V, –5 V, +10 V, and –10 V single outputs.
*Protected by Patent Number 4,644,253.
REV. D
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. 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 companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703 © 2003, Analog Devices, Inc. All rights reserved.






AD588 Datasheet, Funktion
AD588
0.1F
0.1F
NOISE
REDUCTION
Note that a second capacitor is needed in order to implement
the NOISE REDUCTION feature when using the AD588 in
the –10 V mode (Figure 2c.). The NOISE REDUCTION capaci-
tor is limited to 0.1 µF maximum in this mode.
RB
A1
R1
R2
R3
A2
R4
R5
R6
A3
A4
+VS
AD588
–VS
SYSTEM
GROUND
–5V
–10V
+15V
0.1F
SYSTEM
GROUND
0.1F
–15V
Figure 2c. –10 V Output
Trimming the AD588 introduces no additional errors over
temperature, so precision potentiometers are not required.
For single-output voltage ranges, or in cases when BALANCE
ADJUST is not required, Pin 12 should be connected to Pin 11.
If GAIN ADJUST is not required, Pin 5 should be left floating.
NOISE PERFORMANCE AND REDUCTION
The noise generated by the AD588 is typically less than 6 µV p-p
over the 0.1 Hz to 10 Hz band. Noise in a 1 MHz bandwidth is
approximately 600 µV p-p. The dominant source of this noise is
the buried Zener, which contributes approximately 100 nV/Hz.
In comparison, the op amp’s contribution is negligible. Figure 3
shows the 0.1 Hz to 10 Hz noise of a typical AD588.
Figure 4. Effect of 1 µF Noise Reduction Capacitor
on Broadband Noise
TURN-ON TIME
Upon application of power (cold start), the time required for the
output voltage to reach its final value within a specified error
band is the turn-on settling time. Two components normally
associated with this are: time for active circuits to settle and
time for thermal gradients on the chip to stabilize. Figures 5a
and 5b show the turn-on characteristics of the AD588. It
shows the settling to be about 600 µs. Note the absence of any
thermal tails when the horizontal scale is expanded to 2 ms/cm in
Figure 5b.
Figure 5a. Electrical Turn-On
Figure 3. 0.1 Hz to 10 Hz Noise (0.1 Hz to 10 Hz BPF
with Gain of 1000 Applied)
If further noise reduction is desired, an optional capacitor, CN,
may be added between the NOISE REDUCTION pin and ground,
as shown in Figure 2b. This will form a low-pass filter with the
4 kRB on the output of the Zener cell. A 1 µF capacitor will
have a 3 dB point at 40 Hz and will reduce the high frequency
(to 1 MHz) noise to about 200 µV p-p. Figure 4 shows the 1 MHz
noise of a typical AD588 both with and without a 1 µF capacitor.
Figure 5b. Extended Time Scale Turn-On
Output turn-on time is modified when an external noise reduc-
tion capacitor is used. When present, this capacitor presents an
–6– REV. D

6 Page









AD588 pdf, datenblatt
AD588
12-Bit Analog-to-Digital Converter—AD574A
The AD574A is specified for gain drift from 10 ppm/°C to
50 ppm/°C, (depending on grade) using its on-chip reference.
The reference contributes typically 75% of this drift. Therefore,
the total drift using an AD588 to supply the reference can be
improved by a factor of 3 to 4.
Using this combination may result in apparent increases in full-
scale error due to the difference between the on-board reference
by which the device is laser-trimmed and the external reference
with which the device is actually applied. The on-board reference
is specified to be 10 V ± 100 mV, while the external reference is
specified to be 10 V ± 1 mV. This may result in up to 101 mV
of apparent full-scale error beyond the ± 25 mV specified AD574
gain error. External resistors R2 and R3 allow this error to be
nulled. Their contribution to full-scale drift is negligible.
The high output drive capability allows the AD588 to drive up
to six converters in a multiconverter system. All converters will
have gain errors that track to better than ± 5 ppm/°C.
RTD EXCITATION
The resistance temperature detector (RTD) is a circuit element
whose resistance is characterized by a positive temperature
coefficient. A measurement of resistance indicates the measured
temperature. Unfortunately, the resistance of the wires leading
to the RTD often adds error to this measurement. The 4-wire
ohms measurement overcomes this problem. This method uses
two wires to bring an excitation current to the RTD and two
additional wires to tap off the resulting RTD voltage. If these
additional two wires go to a high input impedance measurement
circuit, the effect of their resistance is negligible. Therefore, they
transmit the true RTD voltage.
R
IEXC
R
RTD
I=0
R+
VOUT RRTD
R
I=0
Figure 23. 4-Wire Ohms Measurement
A practical consideration when using the 4-wire ohms technique
with an RTD is the self-heating effect that the excitation current
has on the temperature of the RTD. The designer must choose
the smallest practical excitation current that still gives the desired
resolution. RTD manufacturers usually specify the self-heating
effect of each of their models or types of RTDs.
Figure 24 shows an AD588 providing the precision excitation
current for a 100 RTD. The small excitation current of 1 mA
dissipates a mere 0.1 mW of power in the RTD.
RB
A1
R1
R2
R3
A2
R4
R5
R6
A3
A4
AD588
R1
50
R3
500
20 TURN
R2
61.9
VIN
10V
+VS
–VS
12 8
STS
CS
HIGH
BITS
AO
R/C
CE
AD574A
REF IN
REF OUT
MIDDLE
BITS
LOW
BITS
BIPP OFF
+5V
10VIN
20VIN
ANA COM
+15V
–15V
DIG
COM
Figure 22. AD588/AD574A Connections
–12–
REV. D

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