Datasheet

ADR360/ADR361/ADR363/ADR364/ADR365/ADR366
Rev. D | Page 16 of 20
THEORY OF OPERATION
Band gap references are the high performance solution for low
supply voltage and low power voltage reference applications,
and the ADR36x family is no exception. The uniqueness of
these products lies in their architecture. The ideal zero TC band
gap voltage is referenced to the output, not to ground (see
Figure 32). Therefore, if noise exists on the ground line, it is
greatly attenuated on V
OUT
. The band gap cell consists of the
PNP pair Q53 and Q52 running at unequal current densities.
The difference in V
BE
results in a voltage with a positive TC,
which is amplified by a ratio of
R54
R59
×2
This PTAT voltage, combined with the V
BE
of Q53 and Q52,
produces the stable band gap voltage.
Reduction in the band gap curvature is performed by the ratio
of Resistor R44 and Resistor R59, one of which is linearly
temperature dependent. Precision laser trimming and other
patented circuit techniques are used to further enhance the drift
performance.
R60
Q53
R54
R61
R53
Q52
R58
R59 R44
R50
30kΩ
Q2
05467-024
R101
Q61
R100
Q60
Q1
R48
R49
62kΩ
V
OUT (FORCE)
V
OUT (SENSE)
TRIM
Figure 32. Simplified Schematic
DEVICE POWER DISSIPATION CONSIDERATIONS
The ADR36x family is capable of delivering load currents to
5 mA with an input voltage ranging from 2.348 V (ADR360
only) to 18 V. When this device is used in applications with
large input voltages, care should be taken to avoid exceeding the
specified maximum power dissipation or junction temperature
because it may result in premature device failure. Use the
following formula to calculate a device’s maximum junction
temperature or dissipation:
JA
A
J
D
θ
TT
P
−
=
where:
T
J
and T
A
are the junction and ambient temperatures, respectively.
P
D
is the device power dissipation.
θ
JA
is the device package thermal resistance.
INPUT CAPACITOR
Input capacitors are not required on the ADR36x. There is no
limit for the value of the capacitor used on the input, but a 1 μF
to 10 μF capacitor on the input improves transient response in
applications where the supply suddenly changes. An additional
0.1 μF capacitor in parallel also helps reduce noise from the supply.
OUTPUT CAPACITOR
The ADR36x does not require output capacitors for stability under
any load condition. An output capacitor, typically 0.1 μF, filters
out low level noise voltage and does not affect the operation of
the part. On the other hand, the load transient response can
improve with an additional 1 μF to 10 μF output capacitor placed
in parallel with the 0.1 μF capacitor. The additional capacitor
acts as a source of stored energy for a sudden increase in load
current, and the only parameter that degrades is the turn-on
time. The amount of degradation depends on the size of the
capacitor chosen.