1

+V

S

V

O

GND

Via to ground plane

Via to power plane

2

3

12

LM61

SNIS121J – JUNE 1999 – REVISED NOVEMBER 2016

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Copyright © 1999–2016, Texas Instruments Incorporated

Layout Examples (continued)

A.

1/2 in.2 printed-circuit board with 2 oz copper foil or similar.

Figure 18. Printed-Circuit Board Used for Heat Sink to Generate All Curves

Figure 19. PCB Layout

10.3 Thermal Considerations

The junction-to-ambient thermal resistance is the parameter used to calculate the rise of a device junction

temperature due to its power dissipation. For the LM61, Equation 2 is used to calculate the rise in the die

temperature.

TJ = TA + RθJA × ((+VS × IQ) + (+VS – VO) × IL)

where

•

IQ is the quiescent current

•

ILis the load current on the output

(2)

Table 2 summarizes the rise in die temperature of the LM61 without any loading with a 3.3-V supply, and the

thermal resistance for different conditions.