LT3029 LINER [Linear Technology], LT3029 Datasheet - Page 16

• Manufacturer Part Number: LT3029
• Description: Dual 500mA/500mA Low Dropout, Low Noise, Micropower Linear Regulator
• Manufacturer: LINER [Linear Technology]

LT3029
APPLICATIONS INFORMATION
Calculating Junction Temperature
Example: Channel 1’s output voltage is set to 1.8V. Chan-
nel 2’s output voltage is set to 1.5V. Each channel’s input
voltage is 2.5V. Each channel’s output current range is
0mA to 500mA. The application has a maximum ambient
temperature of 50°C. What is the LT3029’s maximum
junction temperature?
The power dissipated by each channel equals:
where for each output:
I
V
I
So, for output 1:
P = 500mA (2.5V – 1.8V) + 8.5mA (2.5V) = 0.37W
For output 2:
P = 500mA (2.5V – 1.5V) + 8.5mA (2.5V) = 0.52W
The thermal resistance is in the range of 35°C/W to 40°C/W,
depending on the copper area. So, the junction temperature
rise above ambient temperature approximately equals:
The maximum junction temperature then equals the maxi-
mum ambient temperature plus the maximum junction
temperature rise above ambient temperature, or:
16
OUT(MAX)
GND
IN
I
(0.37W + 0.52W) 39°C/W = 34.7°C
T
OUT(MAX)
= 2.5V
JMAX
at (I
OUT
= 50°C + 34.7°C = 84.7°C
= 500mA
(V
= 500mA, V
IN
– V
OUT
) + I
IN
= 2.5V) = 8.5mA
GND
(V
IN
)
Protection Features
The LT3029 regulator incorporates several protection fea-
tures that make it ideal for use in battery-powered circuits.
In addition to the normal protection features associated
with monolithic regulators, such as current limiting and
thermal limiting, the device protects itself against reverse
input voltages and reverse voltages from output to input.
The two regulators have independent inputs, a common
GND pin and are thermally coupled. However, the two
channels of the LT3029 operate independently. Each
channel’s output can be shut down independently, and
a fault condition on one output does not affect the other
output electrically, unless the thermal shutdown circuitry
is activated.
Current limit protection and thermal overload protection
protect the device against current overload conditions at
each output of the LT3029. For normal operation, do not
allow the junction temperature to exceed 125°C (LT3029E/
LT3029I/LT3029MP) or 150°C (LT3029H). The typical ther-
mal shutdown temperature threshold is 165°C and the
circuitry incorporates approximately 5°C of hysteresis.
Each channel’s input withstands reverse voltages of 22V.
Current fl ow into the device is limited to less than 1mA
(typically less than 100μA) and no negative voltage appears
at the respective channel’s output. The device protects
both itself and the load against batteries that are plugged
in backwards.
The LT3029 incurs no damage if either channel’s output
is pulled below ground. If the input is left open-circuit,
or grounded, the output can be pulled below ground by
3029f