LT3050EDDB LINER [Linear Technology], LT3050EDDB Datasheet - Page 17

• Manufacturer Part Number: LT3050EDDB
• Description: 100mA, Low Noise Linear Regulator With Precision Current Limit And Diagnostic Functions
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Thermal Considerations
The LT3050’s maximum rated junction temperature of
125°C limits its power handling capability. Two components
comprise the power dissipated by the device:
GND pin current is determined using the GND Pin Current
curves in the Typical Performance Characteristics section.
Power dissipation equals the sum of the two components
listed above.
The LT3050 regulator has internal thermal limiting that
protects the device during overload conditions. For
continuous normal conditions, do not exceed the maximum
junction temperature of 125°C. Carefully consider all
sources of thermal resistance from junction-to-ambient
including other heat sources mounted in proximity to the
LT3050.
The undersides of the LT3050 DFN and MSOP packages
have exposed metal from the lead frame to the die
attachment. These packages allow heat to directly transfer
from the die junction to the printed circuit board metal
to control maximum operating junction temperature.
The dual-in-line pin arrangement allows metal to extend
beyond the ends of the package on the topside (component
side) of a PCB. Connect this metal to GND on the PCB.
The multiple IN and OUT pins of the LT3050 also assist
in spreading heat to the PCB.
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through-holes also can spread the heat generated by
power devices. The following tables list thermal resistance
as a function of copper area in a fi xed board size. All
measurements were taken in still air on a four-layer FR-4
board with one ounce solid internal planes and two ounce
external trace planes with a total board thickness of 1.6mm.
For further information on thermal resistance and using
thermal information, refer to JEDEC standard JESD51,
notably JESD51-12.
1. Output current multiplied by the input/output
2. GND pin current multiplied by the input voltage:
voltage differential: I
I
GND
• V
IN
OUT
• (V
IN
– V
OUT
), and
Table 1. MSOP Measured Thermal Resistance
Table 2. DFN Measured Thermal Resistance
Calculating Junction Temperature
Example: Given an output voltage of 5V, an input voltage
range of 12V ±5%, a maximum output current range of
75mA and a maximum ambient temperature of 85°C, what
will the maximum junction temperature be?
The power dissipated by the device equals:
where,
So,
Using a DFN package, the thermal resistance ranges from
44°C/W to 49°C/W depending on the copper area. So the
junction temperature rise above ambient approximately
equals:
The maximum junction temperature equals the maximum
ambient temperature plus the maximum junction
temperature rise above ambient or:
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
225 sq mm 2500 sq mm 2500 sq mm
100 sq mm 2500 sq mm 2500 sq mm
TOPSIDE
I
I
V
I
P = 75mA • (12.6V - 5V) + 1.5mA • 12.6V = 0.589W
0.589W • 49°C/W = 28.86°C
T
COPPER AREA
OUT(MAX)
OUT(MAX)
GND
2500 sq mm
1000 sq mm
JMAX
225 sq mm
100 sq mm
IN(MAX)
TOPSIDE
COPPER AREA
at (I
= 85°C + 28.86°C = 113.86°C
= 12.6V
OUT
BACKSIDE
* (V
= 75mA
= 75mA, V
IN(MAX)
BOARD AREA
2500 sq mm
2500 sq mm
2500 sq mm
2500 sq mm
BOARD AREA
– V
IN
OUT
= 12V) = 1.5mA
) + I
(JUNCTION-TO-AMBIENT)
(JUNCTION-TO-AMBIENT)
GND
THERMAL RESISTANCE
THERMAL RESISTANCE
* V
44°C/W
45°C/W
47°C/W
49°C/W
40°C/W
41°C/W
43°C/W
45°C/W
LT3050
IN(MAX)
17
3050f