AD584LH View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD584LH

Pin Programmable Precision Voltage Reference

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 Ω

resistor as shown in Figure 9.

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 ter-

minal directly, provided the gate can withstand the AD584 out-

put voltage plus one volt.

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.

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 volt 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

Figure 10. High Current Precision Supply

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 VIN and VOUT terminals are con-

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 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 character-

–6–

REV. A

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