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TPS7A4501_17 Datasheet, PDF (25/36 Pages) Texas Instruments – Low-Noise Fast-Transient-Response 1.5-A Low-Dropout Voltage Regulators
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TPS7A4501, TPS7A4515, TPS7A4518, TPS7A4525, TPS7A4533
SLVS720F – JUNE 2008 – REVISED NOVEMBER 2015
Thermal Considerations (continued)
Table 4 lists thermal resistance for several different board sizes and copper areas. All measurements were taken
in still air on 1/16-inch FR-4 board with 1-oz copper.
Table 4. Thermal Data (KTT Package, 5-Pin TO-263)
COPPER AREA
TOPSIDE (1)
BACKSIDE
2500 mm2
2500 mm2
1000 mm2
2500 mm2
125 mm2
2500 mm2
BOARD AREA
2500 mm2
2500 mm2
2500 mm2
THERMAL RESISTANCE
(JUNCTION TO AMBIENT)
23°C/W
25°C/W
33°C/W
(1) Device is mounted on topside.
11.3.1 Calculating Junction Temperature
Example: Given an output voltage of 3.3 V, an input voltage range of 4 to 6 V, an output current range of 0 to
500 mA, and a maximum ambient temperature of 50°C, what is the operating junction temperature?
The power dissipated by the device is equal to:
IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX))
where
• IOUT(MAX) = 500 mA
• VIN(MAX) = 6 V
• IGND at (IOUT = 500 mA, VIN = 6 V) = 10 mA
(18)
So,
P = 500 mA × (6 V – 3.3 V) + 10 mA × 6 V = 1.41 W
(19)
Using a KTT package, the thermal resistance is in the range of 23°C/W to 33°C/W, depending on the copper
area. So the junction temperature rise above ambient is approximately equal to:
1.41 W × 28°C/W = 39.5 °C
(20)
The junction temperature rise can then be added to the maximum ambient temperature to find the operating
junction temperature (TJ):
TJ = 50°C + 39.5°C = 89.5°C
(21)
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