AD584L AD [Analog Devices], AD584L Datasheet - Page 6

• Manufacturer Part Number: AD584L
• Description: Pin Programmable Precision Voltage Reference
• Manufacturer: AD [Analog Devices]

AD584
USING THE STROBE TERMINAL
The AD584 has a strobe input which can be used to zero the
output. This unique feature permits a variety of new applica-
tions 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 cur-
rent (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 current should be limited by a 100
resistor as shown in Figure 9.
The strobe terminal will tolerate up to 5 A leakage and its
driver should be capable of sinking 500 A continuous. A low
leakage open collector gate can be used to drive the strobe ter-
minal directly, provided the gate can withstand the AD584 out-
put voltage plus one volt.
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 volt output with up to 4 amperes supplied to the load. The
0.1 F 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 10. High Current Precision Supply
Figure 9. Use of the Strobe Terminal
–6–
The AD584 can also use an NPN or Darlington NPN transistor
to boost its output current. Simply connect the 10 V output ter-
minal 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 con-
figuration. Variable or adjustable outputs (as shown in Figures 1
and 2) may be combined with +5.0 V connection to obtain out-
puts above +5.0 V.
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 coeffi-
cients 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 minimum voltage required to drive the con-
nection is 5 volts.
NEGATIVE REFERENCE VOLTAGES FROM AN AD584
The AD584 can also be used in a two-terminal “Zener” mode
to provide a precision –10 volt, –7.5 volt or –5.0 volt reference.
As shown in Figure 13, the V
nected 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
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
and the supply resistor, R
AD584 is always between 1 mA and 5 mA (between 2 mA and
5 mA for operation beyond +85 C). The temperature character-
Figure 12. A Two-Component Precision Current Limiter
typical to 2 . It is essential to arrange the output load
Figure 11. NPN Output Current Booster
OUT
. With 1 mA flowing through the AD584 in this
S
, so that the net current through the
IN
and V
OUT
terminals are con-
REV. A