AD584
USING THE STROBE TERMINAL
The AD584 can also use an NPN or Darlington NPN transistor
to boost its output current. Simply connect the 10 V output termi-
nal of the AD584 to the base of the NPN booster and take the
output from the booster emitter as shown in Figure 11. The 5.0 V
or 2.5 V pin must connect to the actual output in this configu-
ration. Variable or adjustable outputs (as shown in Figures 1
and 2) may be combined with 5.0 V connection to obtain outputs
above 5.0 V.
The AD584 has a strobe input which can be used to zero the output.
This unique feature permits a variety of new applications in signal
and power conditioning circuits.
Figure 9 illustrates the strobe connection. A simple NPN switch
can be used to translate a TTL logic signal into a strobe of the
output. The AD584 operates normally when there is no current
drawn from Pin 5. Bringing this terminal low, to less than 200 mV,
will allow the output voltage to go to zero. In this mode the AD584
should not be required to source or sink current (unless a 0.7 V
residual output is permissible). If the AD584 is required to sink
a transient current while strobed off, the strobe terminal input cur-
rent should be limited by a 100 Ω resistor as shown in Figure 9.
THE AD584 AS A CURRENT LIMITER
The AD584 represents an alternative to current limiter diodes which
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 12). Of course, the mini-
mum voltage required to drive the connection is 5 V.
The strobe terminal will tolerate up to 5 µA leakage and its driver
should be capable of sinking 500 µA continuous. A low leakage
open collector gate can be used to drive the strobe terminal
directly, provided the gate can withstand the AD584 output
voltage plus 1 V.
Figure 9. Use of the Strobe Terminal
Figure 11. NPN Output Current Booster
PRECISION HIGH CURRENT SUPPLY
The AD584 can be easily connected to a power PNP or power
Darlington PNP device to provide much greater output current
capability. The circuit shown in Figure 10 delivers a precision 10 V
output with up to 4 amperes supplied to the load. The 0.1 µF
capacitor is required only if the load has a significant capacitive
component. If the load is purely resistive, improved high frequency
supply rejection results from removing the capacitor.
Figure 12. A Two-Component Precision Current Limiter
NEGATIVE REFERENCE VOLTAGES FROM AN AD584
The AD584 can also be used in a two-terminal “Zener” mode
to provide a precision –10 V, –7.5 V, or –5.0 V reference. As
shown in Figure 13, the VIN and VOUT 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 VOUT
.
With 1 mA flowing through the AD584 in this mode, a typical
unit will show a 2 mV increase in output level over that produced
in the three-terminal mode. Note also 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,
RS, 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 will be essentially the same as that of a unit used in the
standard three-terminal mode.
Figure 10. High Current Precision Supply
REV. B
–7–
ADI [ ADI ]
