Datasheet

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:
JA
A
J
D
TT
P
θ
−
=
where:
P
D
is the device power dissipation.
T
J
is the device junction temperature.
T
A
is the ambient temperature.
θ
JA
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.