LM340, A Series

13

MOTOROLA ANALOG IC DEVICE DATA

VOLTAGE REGULATOR PERFORMANCE

The performance of a voltage regulator is specified by its

immunity to changes in load, input voltage, power dissipation,

and temperature. Line and load regulation are tested with a

pulse of short duration (< 100

µs) and are strictly a function of

electrical gain. However, pulse widths of longer duration

(> 1.0 ms) are sufficient to affect temperature gradients

across the die. These temperature gradients can cause a

change in the output voltage, in addition to changes caused

by line and load regulation. Longer pulse widths and thermal

gradients make it desirable to specify thermal regulation.

Thermal regulation is defined as the change in output

voltage caused by a change in dissipated power for a

specified time, and is expressed as a percentage output

voltage change per watt. The change in dissipated power can

be caused by a change in either input voltage or the load

current. Thermal regulation is a function of IC layout and die

attach techniques, and usually occurs within 10 ms of a

change in power dissipation. After 10 ms, additional changes

in the output voltage are due to the temperature coefficient of

the device.

Figure 1 shows the line and thermal regulation response of

a typical LM340AT–5.0 to a 10 W input pulse. The variation of

the output voltage due to line regulation is labeled À and the

thermal regulation component is labeled Á. Figure 2 shows

the load and thermal regulation response of a typical

LM340AT–5.0 to a 15 W load pulse. The output voltage

variation due to load regulation is labeled À and the thermal

regulation component is labeled Á.

2

1

2

1

Vout = 5.0 V

Vin = 7.5 V

Iout = 1.0 A

CO = 0

TJ = 25°C

Vin – Vout = 5.0 V

Iout = 100 mA

Figure 1. Line and Thermal Regulation

Figure 2. Load and Thermal Regulation

LM340AT–5.0

Vout = 5.0 V

Vin = 15 V

Iout = 0 A → 1.5 A → 0 A

= Regline = 4.4 mV

t, TIME (2.0 ms/DIV)

1

2

2.0

0

LM340AT–5.0

Vout = 5.0 V

Vin = 8.0 V → 18 V → 8.0 V

Iout = 1.0 A

= Regline = 2.4 mV

t, TIME (2.0 ms/DIV)

1

2

18 V

8.0 V

2

2

Figure 3. Temperature Stability

Figure 4. Output Impedance

1.02

1.00

0.98

–90

–50

–10

30

70

110

150

190

TJ, JUNCTION TEMPERATURE (°C)

100

10–1

10–2

10–3

10–4

1.0

10

100

1.0 k

10 k

100 k

1.0 M

10 M

100 M

f, FREQUENCY (Hz)

1.01

0.99

= Regtherm = 0.0030% VO/W

= Regtherm = 0.0020% VO/W