Data Sheet AD584
Rev. C | Page 9 of 12
The AD584 can also use an NPN or NPN Darlington transistor to
boost its output current. Simply connect the 10 V output terminal
of the AD584 to the base of the NPN booster and take the
output from the booster emitter, as shown in Figure 13. The
5.0V pin or the 2.5V pin must connect to the actual output in
this configuration. Variable or adjustable outputs (as shown in
Figure 3 and Figure 4) can be combined with a 5.0 V connection to
obtain outputs above 5.0 V.
Figure 13. NPN Output Current Booster
THE AD584 AS A CURRENT LIMITER
The AD584 represents an alternative to current limiter diodes
that require factory selection to achieve a desired current. Use of
current limiting diodes often results in temperature coefficients
of 1%/°C. Use of the AD584 in this mode is not limited to a set
current limit; it can be programmed from 0.75 mA to 5 mA
with the insertion of a single external resistor (see Figure 14).
The minimum voltage required to drive the connection is 5 V.
Figure 14. A Two-Component Precision Current Limiter
NEGATIVE REFERENCE VOLTAGES FROM AN AD584
The AD584 can also be used in a 2-terminal Zener mode to
provide a precision −1 0 V, −7.5 V, or −5.0 V reference. As shown in
Figure 15, the V
IN
and V
OUT
terminals are connected together to
the positive supply (in this case, ground). The AD584 COMMON
pin is connected through a resistor to the negative supply. The
output is now taken from the COMMON pin instead of V
OUT
. With
1 mA flowing through the AD584 in this mode, a typical unit
shows a 2 mV increase in the output level over that produced in
3-terminal mode. Also, note that the effective output impedance in
this connection increases from 0.2 Ω typical to 2 Ω. It is essential
to arrange the output load and the supply resistor, R
S
, so that
the net current through the AD584 is always between 1 mA
and 5 mA (between 2 mA and 5 mA for operation beyond 85°C).
The temperature characteristics and long-term stability of the
device is essentially the same as that of a unit used in standard
3-terminal mode.
Figure 15. 2-Terminal, −5 V Reference
The AD584 can also be used in 2-terminal mode to develop a
positive reference. V
IN
and V
OUT
are tied together and to the
positive supply through an appropriate supply resistor. The
performance characteristics are similar to those of a negative
2-terminal connection. The only advantage of this connection
over the standard 3-terminal connection is that a lower primary
supply can be used, as low as 0.5 V above the desired output
voltage. This type of operation requires considerable attention
to load and to the primary supply regulation to ensure that the
AD584 always remains within its regulating range of 1 mA to
5 mA (2 mA to 5 mA for operation beyond 85°C).
10 V REFERENCE WITH MULTIPLYING CMOS DACs
OR ADCs
The AD584 is ideal for application with the AD7533 10-bit
multiplying CMOS DAC, especially for low power applications.
It is equally suitable for the
AD7574 8-bit ADC.
In the standard
hook-up, as shown in Figure 16, the standard output voltages are
inverted by the amplifier/DAC configuration to produce converted
voltage ranges. For example, a +10 V reference produces a 0 V to
−10 V range. If an OP1177 amplifier is used, total quiescent
supply current is typically 2 mA.
Figure 16. Low Power 10-Bit CMOS DAC Application
AD584
1
10.0V
5.0V
2.5V
2
3
8
V+
4
COMMON
DARLINGTON
NPN 2N6057
V
OUT
(5V, 12A
AS SHOWN)
1kΩ
RAW SUPPLY (≈5V > V
OUT
)
00527-014
AD584
1
V
OUT
= 2.5V
2.5V
TAP
3
8
V+
4
COMMON
=
i
+ 0.75mA
2.5V
R
R
LOAD
00527-015
AD584
1
V
OUT
V
REF
–5V
5.0V
TAP
2
8
V+
4
COMMON
–15V
R
S
2.4kΩ
5%
ANALOG
GND
1µF
00527-016
AD584
10.0V
V+
1
8
4
COMMON
+15V
AD7533
4
BIT 1 (MSB)
5
DIGITAL
INPUT
13
16
1
2
BIT 10 (LSB)
15
3
14
V
REF
+15V
–15V
V
OUT
0V TO –10V
R
FB
I
OUT
1
I
OUT
2
COMMON
00527-017
