LM317SSLASHNOPB datasheet(30/51 Pages) TI

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LM117, LM317-N

SNVS774Q – MAY 2004 – REVISED JUNE 2020

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Layout Guidelines (continued)

11.1.1.2.2

Heatsinking the TO-263 (KTT) Package

Figure 39 shows for the TO-263 the measured values of RθJA for different copper area sizes using a typical PCB

with 1-oz. copper and no solder mask over the copper area used for heatsinking.

As shown in Figure 39, increasing the copper area beyond 1 square inch produces very little improvement. It

must also be observed that the minimum value of RθJA for the TO-263 package mounted to a PCB is 32°C/W.

Figure 39. RθJA vs Copper (1-oz.) Area for the TO-263 Package

As a design aid, Figure 40 shows the maximum allowable power dissipation compared to ambient temperature

for the TO-263 device (assuming RθJA is 35°C/W and the maximum junction temperature is 125°C).

Figure 40. Maximum Power Dissipation vs TAMB for the TO-263 Package

11.1.1.2.3

Heatsinking the TO-252 (NDP) Package

If the maximum allowable value for RθJA is found to be ≥ 54°C/W (typical rated value) for the TO-252 package, no

heatsink is needed because the package alone will dissipate enough heat to satisfy these requirements. If the

calculated value for RθJA falls below these limits, a heatsink is required.

As a design aid, Table 1 shows the value of the RθJA of NDP the package for different heatsink area. The copper

patterns that we used to measure these RθJAs are shown in Figure 45. Figure 41 reflects the same test results as

what are in Table 1.

Figure 42 shows the maximum allowable power dissipation versus ambient temperature for the TO-252 device.

Figure 43 shows the maximum allowable power dissipation versus copper area (in2) for the TO-252 device. See

the AN-1028 Maximum Power Enhancement Techniques for Power Packages application note for thermal

enhancement techniques to be used with SOT-223 and TO-252 packages.

LM317S/NOPB Datasheet(PDF) 30 Page - Texas Instruments