ADR318 Analog Devices, Inc., ADR318 Datasheet - Page 9

• Manufacturer Part Number: ADR318
• Description: Precision Low Drift Sot-23 Voltage Reference With Shutdown
• Manufacturer: Analog Devices, Inc.

THEORY OF OPERATION
Band gap references are the high performance solution for low
supply voltage and low power voltage reference applications,
and the ADR318 is no exception. The uniqueness of this lies in
its architecture. By observing
temperature coefficient (TC) band gap voltage is referenced to
the output, not to ground. Therefore, if noise exists on the
ground line, it is greatly attenuated on V
consists of the PNP pair, Q51 and Q52, running at unequal
current densities. The difference in voltage base emitter (V
results in a voltage with a positive TC that is amplified by the
ratio of 2 × (R58/R54). This proportional-to-absolute
temperature (PTAT) voltage, combined with V
Q52, produces the stable band gap voltage.
Reduction in band gap curvature is performed by the ratio of
the resistors R44 and R59, one of which is linearly temperature
dependent. Precision laser-trimming and other patented circuit
techniques are used to further enhance the drift performance.
SHDN
Figure 17. Simplified Schematic
Q1
R59
R54
R60
Q51
Figure 17, the ideal zero
R53
R58
R61
R44
Q52
OUT
R49
R48
. The band gap cell
BE
Q51 and V
V
V
V
GND
IN
OUT(FORCE)
OUT(SENSE)
BE
BE
)
Rev. A | Page 9 of 12
DEVICE POWER DISSIPATION CONSIDERATIONS
The ADR318 is capable of delivering load currents up to 5 mA
with an input voltage that ranges from 2.4 V to 15 V. When this
device is used in applications with high input voltages, care
should be taken to avoid exceeding the specified maximum
power dissipation or junction temperature. Doing so results in
premature device failure. The following formula should be used
to calculate the device’s maximum junction temperature or
dissipation:
where:
T
T
P
θ
SHUTDOWN MODE OPERATION
The ADR318 includes a shutdown feature that is TTL/CMOS
compatible. A logic low or a 0 V condition on the SHDN pin is
required to turn the device off. During shutdown, the output of
the reference becomes a high impedance state where its
potential would then be determined by external circuitry. If the
shutdown feature is not used, the SHDN pin should be
connected to V
JA
D
J
A
= the junction temperature.
= the device power dissipation.
= the ambient temperatures.
= the device package thermal resistance.
P
D
=
T
J
θ
−
JA
IN
T
A
(Pin 2).
ADR318
(4)