ADR3412/ADR3420/ADR3425/ADR3430/ADR3433/ADR3440/ADR3450

Rev. B | Page 19 of 24

THEORY OF OPERATION

BAND GAP

VOLTAGE

REFERENCE

ENABLE

GND FORCE

GND SENSE

Figure 39. Block Diagram

The ADR3412/ADR3425/ADR3430/ADR3433/ADR3440/

ADR3450 use a patented voltage reference architecture to

achieve high accuracy, low temperature coefficient (TC), and

low noise in a CMOS process. Like all band gap references, the

references combine two voltages of opposite TCs to create an

output voltage that is nearly independent of ambient temper-

ature. However, unlike traditional band gap voltage references, the

temperature-independent voltage of the references are arranged

gap voltage of silicon). A corresponding positive-TC voltage is

The key benefit of this technique is that the trimming of the

initial accuracy and TC can be performed without interfering

with one another, thereby increasing overall accuracy across

temperature. Curvature correction techniques further reduce

the temperature variation.

produce stable output voltages of 2.5 V and 5.0 V. The output

buffer can source up to 10 mA and sink up to −3 mA of load

current.

The ADR34xx family leverages Analog Devices patented

DigiTrim technology to achieve high initial accuracy and low

TC, and precision layout techniques lead to very low long-term

drift and thermal hysteresis.

LONG-TERM STABILITY

One of the key parameters of the ADR34xx references is long-

term stability. Regardless of output voltage, internal testing

during development showed a typical drift of approximately

30 ppm after 1000 hours of continuous, nonloaded operation

in a 50°C environment.

It is important to understand that long-term stability is not

guaranteed by design and that the output from the device may

shift beyond the typical 30 ppm specification at any time,

especially during the first 200 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 ADR34xx voltage references are capable of sourcing 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 cur-

rent 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:

]

[W

T

T

P

JA

A

J

D

θ

−

=

where:

Because of 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

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