lt3082ets8 Linear Technology Corporation, lt3082ets8 Datasheet - Page 12

• Manufacturer Part Number: lt3082ets8
• Description: 200ma Single Resistor Low Dropout Linear Regulator
• Manufacturer: Linear Technology Corporation

LT3082
APPLICATIONS INFORMATION
The LT3082 uses a unity-gain follower from the SET pin
to the OUT pin. Therefore, multiple possibilities exist
(besides a SET pin resistor) to set output voltage. For
example, using a high accuracy voltage reference from
SET to GND removes the errors in output voltage due to
reference current tolerance and resistor tolerance. Active
driving of the SET pin is acceptable.
The typical noise scenario for a linear regulator is that the
output voltage setting resistor divider gains up the noise
reference, especially if V
LT3082’s noise advantage is that the unity-gain follower
presents no noise gain whatsoever from the SET pin to the
output. Thus, noise fi gures do not increase accordingly.
Error amplifi er noise is typical 100nV/√Hz (33μV
the 10Hz to 100kHz bandwidth). The error amplifi er’s noise
is RMS summed with the other noise terms to give a fi nal
noise fi gure for the regulator.
Curves in the Typical Performance Characteristics sec-
tion show noise spectral density and peak-to-peak noise
characteristics for both the reference current and error
amplifi er over the 10Hz to 100kHz bandwidth.
Load Regulation
The LT3082 is a fl oating device. No ground pin exists on
the packages. Thus, the IC delivers all quiescent current
and drive current to the load. Therefore, it is not possible
to provide true remote load sensing. The connection resis-
tance between the regulator and the load determines load
regulation performance. The data sheet’s load regulation
specifi cation is Kelvin sensed at the package’s pins. Nega-
tive-side sensing is a true Kelvin connection by returning
the bottom of the voltage setting resistor to the negative
side of the load (see Figure 6).
Connected as shown, system load regulation is the sum
of the LT3082’s load regulation and the parasitic line
resistance multiplied by the output current. To minimize
load regulation, keep the positive connection between the
regulator and load as short as possible. If possible, use
large diameter wire or wide PC board traces.
12
OUT
is much greater than V
RMS
REF
. The
over
Thermal Considerations
The LT3082’s internal power and thermal limiting circuitry
protects itself under overload conditions. For continuous
normal load conditions, do not exceed the 125°C maximum
junction temperature. Carefully consider all sources of
thermal resistance from junction-to-ambient. This includes
(but is not limited to) junction-to-case, case-to-heat sink
interface, heat sink resistance or circuit board-to-ambient
as the application dictates. Consider all additional, adjacent
heat generating sources in proximity on the PCB.
Surface mount packages provide the necessary heatsinking
by using the heat spreading capabilities of the PC board,
copper traces and planes. Surface mount heat sinks, plated
through-holes and solder-fi lled vias can also spread the
heat generated by power devices.
Junction-to-case thermal resistance is specifi ed from
the IC junction to the bottom of the case directly, or
the bottom of the pin most directly, in the heat path.
This is the lowest thermal resistance path for heat fl ow.
Only proper device mounting ensures the best possible
thermal fl ow from this area of the package to the heat
sinking material.
Note that the Exposed Pad of the DFN package and the
tab of the SOT-223 package is electrically connected to
the output (V
Figure 6. Connections for Best Load Regulation
IN
3082 F06
SET
OUT
10μA
).
+
–
LT3082
R
SET
OUT
RESISTANCE
PARASITIC
R
R
R
P
P
P
LOAD
3082f