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AD580K

2.5 V IC Reference High Precision

Analog Devices 

AD580

ABSOLUTE MAXIMUM RATINGS

Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 V

Power Dissipation @ +25°C

Ambient Temperature . . . . . . . . . . . . . . . . . . . . . . . 350 mW

Derate above +25°C . . . . . . . . . . . . . . . . . . . . . . . 2.8 mW/°C

Lead Temperature (Soldering 10 sec) . . . . . . . . . . . . . +300°C

Thermal Resistance

Junction-to-Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100°C

Junction-to-Ambient . . . . . . . . . . . . . . . . . . . . . . . 360°C/W

AD580 CHIP DIMENSIONS

AND PAD LAYOUT

Dimensions shown in inches and (mm).

THEORY OF OPERATION

The AD580 family (AD580, AD581, AD584, AD589) uses

the “bandgap” concept to produce a stable, low temperature

coefficient voltage reference suitable for high accuracy data ac-

quisition components and systems. The device makes use of the

underlying physical nature of a silicon transistor base-emitter

voltage in the forward-biased operating region. All such transis-

tors have approximately a –2 mV/°C temperature coefficient,

unsuitable for use directly as a low TC reference; however,

extrapolation of the temperature characteristic of any one of

these devices to absolute zero (with emitter current proportional

to absolute temperature) reveals that it will go to a VBE of 1.205

volts at 0K, as shown in Figure 1. Thus, if a voltage could be

developed with an opposing temperature coefficient to sum with

VBE to total 1.205 volts, a zero-TC reference would result and

operation from a single, low voltage supply would be possible.

The AD580 circuit provides such a compensating voltage, V1 in

Figure 2, by driving two transistors at different current densities

and amplifying the resulting VBE difference (∆VBE—which now

has a positive TC); the sum (VZ) is then buffered and amplified

up to 2.5 volts to provide a usable reference-voltage output. Fig-

ure 3 is the schematic diagram of the AD580.

The AD580 operates as a three-terminal reference, which means

that no additional components are required for biasing or cur-

rent setting. The connection diagram, Figure 4 is quite simple.

The AD580 is also available in chip form. Consult the factory

for specifications and applications information.

Figure 1. Extrapolated Variation of Base-Emitter Voltage

with Temperature (IEαT), and Required Compensation,

Shown for Two Different Devices

REV. A

Figure 2. Basic Bandgap-Reference Regulator Circuit

–3–

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