THERMAL REGULATION

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 espe-

cially severe since the 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 coeffi-

cient, 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 volt-

age regulator is defined as the percentage change of V

per watt, within the first 10 ms after a step of power is ap-

plied. The LM133’s specification is 0.01%/W, max.

In

Figure 1, a typical LM133’s output drifts only 2 mV (or

0.02% of V

ms. This performance is thus well inside the specification

limit of 0.01%/Wx20W = 0.2% max. When the 20W pulse is

ended, the thermal regulation again showsa2mV step as

the LM133 chip cools off. Note that the load regulation error

of about 1 mV (0.01%) is additional to the thermal regulation

error. In

Figure 2, when the 20W pulse is applied for 100 ms,

the output drifts only slightly beyond the drift in the first 10

ms, and the thermal error stays well within 0.1% (10 mV).

Adjustable Lab Voltage Regulator

DS009065-12

Adjustable Current Regulator

DS009065-13

Ω≤ R1 ≤ 24Ω

DS009065-14

FIGURE 1.

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