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LM137

NEGATIVE VOLTAGE REGULATORS THREE-TERMINAL ADJUSTABLE

STMicroelectronics 

LM137-LM237-LM337

THERMAL REGULATION

When power is dissipated in an IC, a temperature

gradient occurs across the IC chip affecting the in-

dividual 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 tempera-

ture gradients on output voltage (in percentage out-

put change) per watt of power change in a specified

time. Thermal regulation error is independent of

electrical regulation or temperature coefficient, and

occurs within 5ms to 50ms after a change in power

dissipation. Thermal regulation depends on IC

layout as well as electrical design. The thermal regu-

lation of a voltage regulator is defined as the per-

centage change of VO, per watt, within the first 10ms

after a step of power, is applied.

Figure 1.

The LM137 specification is 0.02 %/W max.In figure

1, a typical LM337’s output drifts only 3mV for 0.03%

of VO = – 10V) when a 10W pulse is applied for

10ms. This performance is thus well inside the spe-

cification limit of 0.02%/W x 10W = 0.2% max. When

the 10W pulse is ended the thermal regulation again

shows a 3mV step as the LM137 chip cools off.

Note that the load regulation error of about

8mV(0.08%) is additional to the thermal regulation

error.

In figure 2, when the 10W pulse is applied for

100ms, the output drifts only slightly beyond the drift

in the first 10ms and the thermal error stays well

within 0.1% (10mV).

Figure 2.

LM 337, V0 = – 10V

VI – V0 = – 40V

IL = 0A → 0.25A → 0A

Vertical sensitivity 5mV/div.

LM 337, V0 = – 10V

VI – V0 = – 40V

IL = 0A → 0.25A → 0A

Horizontal sensitivity 20msN/div.

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