AD587
NEGATIVE REFERENCE VOLTAGE FROM AN AD587
The AD587 can be used to provide a precision –10.000 V output
as shown in Figure 11. The +VIN pin is tied to at least a +3.5 V
supply, the output pin is grounded, and the AD587 ground pin is
connected through a resistor, RS, to a –15 V supply. The –10 V
output is now taken from the ground pin (Pin 4) instead of
VOUT. It is essential to arrange the output load and the supply
resistor RS so that the net current through the AD587 is between
2.5 mA and 10.0 mA. The temperature characteristics and long-
term stability of the device will be essentially the same as that of
a unit used in the standard +10 V output configuration.
The AD587 can also be used as a precision reference for multi-
ple DACs. Figure 13 shows the AD587, the AD7628 dual DAC,
and the AD712 dual op amp hooked up for single-supply opera-
tion to produce 0 V to –10 V outputs. Because both DACs are
on the same die and share a common reference and output
op amps, the DAC outputs will exhibit similar gain TCs.
+15V
+15V
0.1ꢃF
V
IN
RFB A
V
REFA
OUT A
V
OUT
DAC A
V
A =
3.5V →26V
OUT
0TO –10V
AD587
GND
AGND
RFB B
DB0
DB7
DATA
INPUTS
AD7628
AD712
2
V
IN
OUT B
18
V
DAC B
DGND
V
OUT
REFB
6
V
B =
OUT
0TO –10V
AD587
GND
4
←I
L
–10V
Figure 13. AD587 as a 10 V Reference for a CMOS Dual DAC
1nF
R
S
Precision Current Source
5V
2.5mA <
– I < 10mA
L
The design of the AD587 allows it to be easily configured as a
current source. By choosing the control resistor RC in Figure 14,
the user can vary the load current from the quiescent current
(2 mA typically) to approximately 10 mA.
R
–15V
S
Figure 11. AD587 as a Negative 10 V Reference
USING THE AD587 WITH CONVERTERS
The AD587 is an ideal reference for a wide variety of 8-, 12-,
14-, and 16-bit ADCs and DACs. Several representative examples
follow.
+V
IN
2
V
IN
10 V Reference with Multiplying CMOS DACs or ADCs
The AD587 is ideal for applications with 10-bit and 12-bit
multiplying CMOS DACs. In the standard hookup, as shown in
Figure 12, the AD587 is paired with the AD7545 12-bit multi-
plying DAC and the AD711 high speed BiFET op amp. The
amplifier DAC configuration produces a unipolar 0 V to –10 V
output range. Bipolar output applications and other operating
details can be found in the individual product data sheets.
10V
V
6
I
=
L
+ I
BIAS
OUT
R
C
R
500ꢂ
MIN
C
AD587
GND
4
Figure 14. Precision Current Source
+15V
R2
+15V
0.1ꢃF
10kꢂ
+15V
0.1ꢃF
C1
33pF
V
IN
R
V
FB
DD
AD587
OUT1
V
V
V
OUT
REF
OUT
AD711K
0.1ꢃF
0TO
–
10V
AGND
TRIM
GND
AD7545K
DGND
DB11–DB0
–15V
Figure 12. Low Power 12-Bit CMOS DAC Application
REV. F
–7–
ADI [ ADI ]
