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 power dissipation is large. Thermal regu-

lation 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 inde-

pendent of electrical regulation or temperature coefficient,

and occurs within 5 ms to 50 ms after a change in power dis-

sipation. Thermal regulation depends on IC layout as well as

electrical design. The thermal regulation of a voltage regula-

tor is defined as the percentage change of V

within the first 10 ms after a step of power is applied. The

LM137HV’s specification is 0.02%/W, max.

In

Figure 1, a typical LM137HV’s output drifts only 3 mV (or

0.03% of V

10 ms. This performance is thus well inside the specification

limit of 0.02%/W x 10W = 0.2% max. When the 10W pulse is

ended, the thermal regulation again showsa3mV step as

the LM137HV chip cools off. Note that the load regulation er-

ror of about 8 mV (0.08%) is additional to the thermal regu-

lation error. In

Figure 2, when the 10W 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).

DS009066-3

Vertical sensitivity, 5 mV/div

FIGURE 1.

DS009066-4

Horizontal sensitivity, 20 ms/div

FIGURE 2.

TO-3

Metal Can Package

DS009066-5

Bottom View

Order Number LM137HVK/883, LM137HVK-QMLV, or

SMD #7703404

See NS Package Number K02C

Order Number LM337HVK STEEL

See NS Package Number K02A

TO-39

Metal Can Package

DS009066-6

Bottom View

Order Number LM137HVH/883, LM137HVH-QMLV, SMD

#7703404

or LML337HVH

See NS Package Number H03A

www.national.com

4