TPS75801_15 Datasheet, PDF (14/26 Pages) Texas Instruments – FAST-TRANSIENT RESPONSE, 3A, LOW-DROPOUT VOLTAGE REGULATORS

TPS75801, TPS758A01
TPS75815, TPS75818
TPS75825, TPS75833
SLVS330F – JUNE 2001 – REVISED APRIL 2007
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THERMAL INFORMATION (continued)
TO-220 Power Dissipation
The TO-220 package provides an effective means of managing power dissipation in through-hole applications.
The TO-220 package dimensions are provided in the mechanical drawings at the end of this data sheet. A
heatsink can be used with the TO-220 package to effectively lower the junction-to-ambient thermal resistance.
To illustrate, the TPS75825 in a TO-220 package was chosen. For this example, the average input voltage is
3.3V, the average output voltage is 2.5V, the average output current is 3A, the ambient temperature +55°C, the
air flow is 150 LFM, and the operating environment is the same as documented below. Neglecting the quiescent
current, the maximum average power is:
P_D max + (3.3 * 2.5) V 3A + 2.4W
(7)
Substituting T_Jmax for T_J in Equation 6 results in Equation 8:
R_QJA
max
+
(125 * 55)°C
2.4W
+
29°CńW
(8)
From Figure 23, R_ΘJA vs Heatsink Thermal Resistance, a heatsink with R_ΘSA = 22°C/W is required to dissipate
2.4W. The model operating environment used in the computer model to construct Figure 23 consisted of a
standard JEDEC High-K board (2S2P) with a 1-ounce internal copper plane and ground plane. Since the
package pins were soldered to the board, 450mm² of the board was modeled as a heatsink. Figure 24 shows
the side view of the operating environment used in the computer model.
65
Natural Convection
55
Air Flow = 150 LFM
45
Air Flow = 250 LFM
Air Flow = 500 LFM
35
25
15
No Heatsink
5
25
20
15
10
5
0
R_θSA − Heatsink Thermal Resistance − °C/W
Figure 23. Thermal Resistance vs Heatsink Thermal Resistance
14
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