LT3023 LINER [Linear Technology], LT3023 Datasheet - Page 12

• Manufacturer Part Number: LT3023
• Description: Dual 100mA, Low Dropout, Low Noise, Micropower Regulator
• Manufacturer: LINER [Linear Technology]

LT3023
APPLICATIONS
Calculating Junction Temperature
Example: Given an output voltage on the first channel of
3.3V, an output voltage of 2.5V on the second channel, an
input voltage range of 4V to 6V, output current ranges of
0mA to 100mA for the first channel and 0mA to 50mA for
the second channel, with a maximum ambient tempera-
ture of 50 C, what will the maximum junction temperature
be?
The power dissipated by each channel of the device will be
equal to:
where (for the first channel):
so:
and (for the second channel):
so:
The thermal resistance will be in the range of 40 C/W to
60 C/W depending on the copper area. So the junction
temperature rise above ambient will be approximately
equal to:
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
Protection Features
The LT3023 regulator incorporates several protection
features which makes it ideal for use in battery-powered
circuits. In addition to the normal protection features
associated with monolithic regulators, such as current
12
I
I
V
I
P1 = 100mA(6V – 3.3V) + 2mA(6V) = 0.28W
I
V
I
P2 = 50mA(6V – 2.5V) + 1mA(6V) = 0.18W
(0.28W + 018W)(60 C/W) = 27.8 C
T
OUT(MAX)
OUT(MAX)
GND
OUT(MAX)
GND
JMAX
IN(MAX)
IN(MAX)
at (I
at (I
= 50 C + 27.8 C = 77.8 C
= 6V
= 6V
OUT
OUT
(V
= 100mA
= 50mA
IN(MAX)
= 100mA, V
= 50mA, V
U
– V
INFORMATION
OUT
U
IN
IN
) + I
= 6V) = 1mA
= 6V) = 2mA
GND
W
(V
IN(MAX)
)
U
limiting and thermal limiting, the devices are protected
against reverse input voltages, reverse output 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
20V. Current flow into the device will be limited to less than
1mA (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 output of the LT3023 can be pulled below ground
without damaging the device. If the input is left open circuit
or grounded, the output can be pulled below ground by
20V. The output will act like an open circuit; no current will
flow out of the pin. If the input is powered by a voltage
source, the output will source the short-circuit current of
the device and will protect itself by thermal limiting. In this
case, grounding the SHDN1/SHDN2 pins will turn off the
device and stop the output from sourcing the short-circuit
current.
The ADJ1 and ADJ2 pins 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 ADJ1 and
ADJ2 pins 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.
In situations where the ADJ1 and ADJ2 pins are connected
to a resistor divider that would pull the pins above their 7V
clamp voltage if the output is pulled high, the ADJ1/ADJ2
pin input current must be limited to less than 5mA. For
example, a resistor divider is used to provide a regulated
1.5V output from the 1.22V reference when the output is
forced to 20V. The top resistor of the resistor divider must
be chosen to limit the current into the ADJ pin to less than
5mA when the ADJ1/ADJ2 pin is at 7V. The 13V difference
between output and ADJ1/ADJ2 pin divided by the 5mA
maximum current into the ADJ1/ADJ2 pin yields a mini-
mum top resistor value of 2.6k.
3023f