LT3010 LINER [Linear Technology], LT3010 Datasheet - Page 11

• Manufacturer Part Number: LT3010
• Description: 50mA, 3V to 80V Low Dropout Micropower Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
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 50mA 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 26 C to 38 C.
P1(48V in, 5mA load) = 5mA • (48V – 5V)
P2(48V in, 50mA load) = 50mA • (48V – 5V)
P3(72V in, 5mA load) = 5mA • (72V – 5V)
P4(72V in, 50mA load) = 50mA • (72V – 5V)
76% operation at P1, 19% for P2, 4% for P3, and
P
+ 1%(3.42W) = 0.64W
T
EFF
JMAX
= 76%(0.23W) + 19%(2.20W) + 4%(0.35W)
= 50 C + 65.5 C = 115.5 C
U
U
+ (200 A • 48V) = 0.23W
+ (200 A • 72V) = 0.35W
+ (1mA • 48V) = 2.20W
+ (1mA • 72V) = 3.42W
1% for P4.
W
U
Protection Features
The LT3010 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 100 A) 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 of the adjustable device 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 refer-
ence voltage will cause the device to try and force the
current limit current out of the output. This will cause the
output to go to a unregulated high voltage. Pulling the ADJ
pin above the reference voltage will turn off all output
current.
LT3010/LT3010-5
11
3010f