ADR360A AD [Analog Devices], ADR360A Datasheet - Page 16

• Manufacturer Part Number: ADR360A
• Description: Low Power, Low Noise Voltage References with Sink/Source Capability
• Manufacturer: AD [Analog Devices]

ADR360/ADR361/ADR363/ADR364/ADR365/ADR366
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
PNP pair Q53 and Q52 running at unequal current densities.
The difference in V
which is amplified by a ratio of
This PTAT voltage, combined with the V
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.
2×
R59
R54
Q53
R59
R54
R60
Figure 32. Simplified Schematic
BE
R53
results in a voltage with a positive TC,
OUT
R58
R44
R61
Q2
. The band gap cell consists of the
Q52
Q61
R101
R100
Q1
Q60
BE
s of Q53 and Q52,
30kΩ
R48
R50
R49
62kΩ
V
V
OUT (FORCE)
OUT (SENSE)
TRIM
Rev. A | Page 16 of 20
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 could result in premature device failure. Use the
following formula to calculate a device’s maximum junction
temperature or dissipation:
In this equation, T
ambient temperatures, P
θ
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 any 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 in parallel. A capacitor here acts as a source of stored
energy for a sudden increase in load current. The only
parameter that degrades by adding an output capacitor is the
turn-on time. The degradation depends on the size of the
capacitor chosen.
JA
is the device package thermal resistance.
P
D
=
T
J
θ
−
JA
T
A
J
and T
D
A
is the device power dissipation, and
are, respectively, the junction and