REF191 datasheet(30/32 Pages) AD

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ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550

Data Sheet

Rev. 0 | Page 30 of 32

THEORY OF OPERATION

The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/

ADR4550 series of references uses a unique core topology for

extremely high accuracy, stability, and noise performance.

Three parameters contribute to the accuracy of the dc output of

a voltage reference: initial accuracy, temperature coefficient, and

long-term drift. With an outstanding guaranteed initial error of

0.02% and a low temperature coefficient of 2 ppm/°C maximum,

this series of voltage references is perfect for high precision

applications. The industry-leading long-term stability of the

devices means that systems need less frequent field calibration

and that there is a reduction in the costly preshipment system

burn-in time.

LONG-TERM DRIFT

One of the key parameters of the ADR4520/ADR4525/ADR4530/

ADR4533/ADR4540/ADR4550 references is long-term

stability—the output drift over time that the device is powered

up. Regardless of output voltage, internal testing during

development showed a typical drift of approximately 25 ppm

after 1000 hours of continuous, nonloaded operation in a 60°C

extremely stable temperature controlled environment.

Note that the majority of the long-term drift typically occurs in

the first 200 hours to 300 hours of operation. For systems that

require highly stable output voltages over long periods of time,

the designer should consider burning in the devices prior to use

to minimize the amount of output drift exhibited by the

reference over time. See the AN-713 Application Note, The

Effect of Long-Term Drift on Voltage References, at www.analog.com

for more information regarding the effects of long-term drift

and how it can be minimized.

POWER DISSIPATION

The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/

ADR4550 voltage references are capable of sourcing and sinking

up to 10 mA of load current at room temperature across the rated

input voltage range. However, when used in applications subject

to high ambient temperatures, the input voltage and load current

should be carefully monitored to ensure that the device does not

exceeded its maximum power dissipation rating. The maximum

power dissipation of the device can be calculated via the

following equation:

−

where:

PD is the device power dissipation.

TJ is the device junction temperature.

TA is the ambient temperature.

θJA is the package (junction-to-air) thermal resistance.

Due to this relationship, acceptable load current in high

temperature conditions may be less than the maximum current

sourcing capability of the device. In no case should the part be

operated outside of its maximum power rating because doing so

may result in premature failure or permanent damage to the device.

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