Datasheet

LT3030
15
3030fa
For more information www.linear.com/LT3030
applicaTions inForMaTion
1. Output current multiplied by the input/output voltage
differential: (I
OUT
)(V
IN
– V
OUT
), and
2.GND pin current multiplied by the input voltage:
(I
GND
)(V
IN
).
Ground pin current is found by examining the GND Pin
Current curves in the Typical Performance Characteristics
section.
Power dissipation for each channel equals the sum of the
two components listed above. Total power dissipation for
the LT3030 equals the sum of the power dissipated by
each channel.
The LT3030’s internal thermal shutdown circuitry
protects both channels of the device if either channel
experiences an overload or fault condition. Activation
of the thermal shutdown circuitry turns both channels
off. If the overload or fault condition is removed, both
outputs are allowed to turn back on. For continu-
ous normal conditions, do not exceed the maximum
junction temperature rating of 125°C (LT3030E/LT3030I)
or 150°C (LT3030H/LT3030MP).
Carefully consider all sources of thermal resistance from
junction-to-ambient, including additional heat sources
mounted in proximity to the LT3030. For surface mount
devices, use the heat spreading capabilities of the PC board
and its copper traces to accomplish heat sinking. Copper
board stiffeners and plated
through-holes can also spread
the heat generated by power devices.
The
following tables list thermal resistance as a function of
copper area in a fixed board size. All measurements were
taken in still air on a four-layer FR-4 board with 1oz solid
internal planes, and 2oz external trace planes with a total
board thickness of 1.6mm. For further information on ther-
mal resistance and using thermal information, refer to JEDEC
standard JESD51, notably JESD 51-7 and JESD 51-12.
Table 2. UFD Package, 28-Lead QFN
COPPER AREA
BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)TOPSIDE* BACKSIDE
2500mm
2
2500mm
2
2500mm
2
30°C/W
1000mm
2
2500mm
2
2500mm
2
32°C/W
225mm
2
2500mm
2
2500mm
2
33°C/W
100mm
2
2500mm
2
2500mm
2
35°C/W
*Device is mounted on topside.
Table 3. FE Package, 20-Lead TSSOP
COPPER AREA
BOARD AREA
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)TOPSIDE* BACKSIDE
2500mm
2
2500mm
2
2500mm
2
25°C/W
1000mm
2
2500mm
2
2500mm
2
27°C/W
225mm
2
2500mm
2
2500mm
2
28°C/W
100mm
2
2500mm
2
2500mm
2
32°C/W
*Device is mounted on topside.
The junction-to-case thermal resistance (θ
JC
), measured
at the exposed pad on the back of the die, is 3.4°C/W for
the QFN package, and 10°C/W for the TSSOP package.
Calculating Junction Temperature
Example: Channel 1’s output voltage is set to 1.8V.
Channel 2’s output voltage is set to 1.5V. Each channel’s
input voltage is 2.5V. Channel 1’s output current range
is 0mA to 750mA. Channel 2’s output current range is
0mA to 250mA. The application has a maximum ambient
temperature of 50°C. What is the LT3030’s maximum
junction temperature?
The power dissipated by each channel equals:
I
OUT(MAX)
(V
IN
– V
OUT
) + I
GND
(V
IN
)
where for output 1:
I
OUT(MAX)
= 750mA
V
IN
= 2.5V
I
GND
at (I
OUT
= 750mA, V
IN
= 2.5V) = 13mA
For output 2:
I
OUT(MAX)
= 250mA
V
IN
= 2.5V
I
GND
at (I
OUT
= 250mA, V
IN
= 2.5V) = 4.5mA
So, for output 1:
P = 750mA (2.5
V – 1.8V) + 13mA (2.5V) = 0.56W
For output 2:
P = 250mA (2.5V – 1.5V) + 4.5mA (2.5V) = 0.26W
The thermal resistance is in the range of 25°C/W to 35°C/W,
depending on the copper area. So, the junction temperature
rise above ambient temperature approximately equals:
(0.56W + 0.26W) 30°C/W = 24.6°C