3021 Ver la hoja de datos (PDF) - Linear Technology
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3021 Datasheet PDF : 16 Pages
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LT3021/LT3021-1.2/
LT3021-1.5/LT3021-1.8
APPLICATIO S I FOR ATIO
The LT3021 regulator has internal thermal limiting (with
hysteresis) designed to protect the device during overload
conditions. For normal continuous conditions, do not
exceed the maximum junction temperature rating of 125°C.
Carefully consider all sources of thermal resistance from
junction to ambient including other heat sources mounted
in proximity to the LT3021.
The underside of the LT3021 DH package has exposed metal
(14mm2) from the lead frame to where the die is attached.
This allows 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 ar-
rangement allows metal to extend beyond the ends of the
package on the topside (component side) of a PCB. Con-
nect this metal to GND on the PCB. The multiple IN and OUT
pins of the LT3021 also assist in spreading heat to the PCB.
The LT3021 S8 package has pin 4 fused with the lead
frame. This also allows heat to transfer from the die to the
printed circuit board metal, therefore reducing the thermal
resistance. Copper board stiffeners and plated through-
holes can also be used to spread the heat generated by
power devices.
The following tables list thermal resistance for several
different board sizes and copper areas for two different
packages. Measurements were taken in still air on 3/32"
FR-4 board with one ounce copper.
Table 1. Measured Thermal Resistance For DH Package
COPPER AREA
THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm2
900mm2
225mm2
100mm2
50mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
30°C/ W
35°C/ W
50°C/ W
55°C/ W
65°C/ W
Table 2. Measured Thermal Resistance For S8 Package
COPPER AREA
TOPSIDE* BACKSIDE
2500mm2 2500mm2
1000mm2 2500mm2
225mm2 2500mm2
100mm2 2500mm2
50mm2 2500mm2
BOARD AREA
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
70°C/ W
70°C/ W
78°C/ W
84°C/ W
96°C/ W
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 1.2V, an input voltage
range of 1.8V ±10%, an output current range of 1mA to
500mA, and a maximum ambient temperature of 70°C,
what will the maximum junction temperature be for an
application using the DH package?
The power dissipated by the device is equal to:
IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX))
where
IOUT(MAX) = 500mA
VIN(MAX) = 1.98V
IGND at (IOUT = 500mA, VIN = 1.98V) = 10mA
so
P = 500mA(1.98V – 1.2V) + 10mA(1.98V) = 0.41W
The thermal resistance is in the range of 35°C/W to
70°C/W depending on the copper area. So the junction
temperature rise above ambient is approximately equal to:
0.41W(52.5°C/W) = 21.5°C
The maximum junction temperature equals the maximum
junction temperature rise above ambient plus the maxi-
mum ambient temperature or:
TJMAX = 21.5°C + 70°C = 91.5°C
Protection Features
The LT3021 incorporates several protection features that
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 also protects against reverse-
input voltages, reverse-output voltages and reverse
output-to-input voltages.
Current limit protection and thermal overload protection
protect the device against current overload conditions at
the output of the device. For normal operation, do not
exceed a junction temperature of 125°C.
The IN pins of the device withstand reverse voltages of
10V. The LT3021 limits current flow to less than 1µA and
no negative voltage appears at OUT. The device protects
both itself and the load against batteries that are plugged
in backwards.
3021fa
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