lt3014bes5-trpbf Linear Technology Corporation, lt3014bes5-trpbf Datasheet - Page 10

• Manufacturer Part Number: lt3014bes5-trpbf
• Description: 20ma, 3v To 80v Low Dropout Micropower Linear Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT3014
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
Example 2: Given an output voltage of 5V, an input voltage
of 48V that rises to 72V for 5ms(max) out of every 100ms,
and a 5mA load that steps to 20mA for 50ms out of every
250ms, what is the junction temperature rise above ambi-
ent? Using a 500ms period (well under the time constant
of the board), power dissipation is as follows:
Operation at the different power levels is as follows:
With a thermal resistance in the range of 40°C/W to
62°C/W, this translates to a junction temperature rise
above ambient of 20°C.
10
P1(48V in, 5mA load) = 5mA • (48V – 5V)
P2(48V in, 20mA load) = 20mA • (48V – 5V)
P3(72V in, 5mA load) = 5mA • (72V – 5V)
P4(72V in, 20mA load) = 20mA • (72V – 5V)
76% operation at P1, 19% for P2, 4% for P3, and
P
+ 1%(1.38W) = 0.36W
T
EFF
JMAX
= 76%(0.22W) + 19%(0.89W) + 4%(0.34W)
= 50°C + 26°C = 76°C
U
U
+ (100µA • 48V) = 0.22W
+ (100µA • 72V) = 0.34W
+ (0.55mA • 48V) = 0.89W
+ (0.55mA • 72V) = 1.38W
1% for P4.
W
U
Protection Features
The LT3014 incorporates several protection features which
make it ideal for use in battery-powered circuits. In addi-
tion to the normal protection features associated with
monolithic regulators, such as current limiting and ther-
mal limiting, the device is protected against reverse-input
voltages, and reverse voltages from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
80V. Current flow into the device will be limited to less than
6mA (typically less than 100µA) and no negative voltage
will appear at the output. The device will protect both itself
and the load. This provides protection against batteries
which can be plugged in backward.
The ADJ pin can be pulled above or below ground by as
much as 7V without damaging the device. If the input is left
open circuit or grounded, the ADJ pin will act like an open
circuit when pulled below ground, and like a large resistor
(typically 100k) in series with a diode when pulled above
ground. If the input is powered by a voltage source, pulling
the ADJ pin below the reference voltage will cause the
device to current limit. This will cause the output to go to
an unregulated high voltage. Pulling the ADJ pin above the
reference voltage will turn off all output current.
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