LM317L-N_16 Datasheet, PDF (27/37 Pages) Texas Instruments – 3-Terminal Adjustable Regulator

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Layout Examples (continued)
LM317L-N
SNVS775K – MARCH 2000 – REVISED APRIL 2016
Figure 45. Layout Example (TO-220)
10.3 Thermal Considerations
When power is dissipated in an IC, a temperature gradient occurs across the IC chip affecting the individual IC
circuit components. With an IC regulator, this gradient can be especially severe since power dissipation is large.
Thermal regulation is the effect of these temperature gradients on output voltage (in percentage output change)
per watt of power change in a specified time. Thermal regulation error is independent of electrical regulation or
temperature coefficient, and occurs within 5 ms to 50 ms after a change in power dissipation. Thermal regulation
depends on IC layout as well as electrical design. The thermal regulation of a voltage regulator is defined as the
percentage change of V_OUT, per watt, within the first 10 ms after a step of power is applied. The LM317L-N
specification is 0.2%/W, maximum.
In Figure 12, a typical output of the LM317L-N changes only 7 mV (or 0.07% of V_OUT = −10 V) when a 1-W pulse
is applied for 10 ms. This performance is thus well inside the specification limit of 0.2%/W × 1 W = 0.2%
maximum. When the 1-W pulse is ended, the thermal regulation again shows a 7-mV change as the gradients
across the LM317L-N chip die out.
NOTE
The load regulation error of about 14 mV (0.14%) is additional to the thermal regulation
error.
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