Datasheet

Thermal regulation LM137, LM337
10/18 Doc ID 2167 Rev 4
6 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
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
O
, per watt, within the first 10ms after a step of power, is applied.
The LM137 specification is 0.02%/W max. In Figure 1, a typical LM337’s output drifts only 3
mV for 0.03% of V
O
= – 10 V) when a 10 W pulse is applied for 10 ms. This performance is
thus well inside the specification limit of 0.02%/W x 10 W = 0.2% max. When the 10 W pulse
is ended the thermal regulation again shows a 3 mV step as the LM137 chip cools off. Note
that the load regulation error of about 8 mV (0.08%) is additional to the thermal regulation
error.
In Figure 2, when the 10 W 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).