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
V
out
, OUTPUT
∆
I
out
, OUTPUT
V
out
, OUTPUT
∆
V
in
, INPUT
V
out
= 5.0 V
V
in
= 7.5 V
I
out
= 1.0 A
C
O
= 0
T
J
= 25
°
C
V
in
– V
out
= 5.0 V
I
out
= 100 mA
Figure 1. Line and Thermal Regulation Figure 2. Load and Thermal Regulation
LM340AT–5.0
V
out
= 5.0 V
V
in
= 15 V
I
out
= 0 A
→
1.5 A
→
0 A
= Reg
line
= 4.4 mV
t, TIME (2.0 ms/DIV)
CURRENT (A) VOLTAGE DEVIATION (V)
(2.0 mV/DIV)
1
2
2.0
0
LM340AT–5.0
V
out
= 5.0 V
V
in
= 8.0 V
→
18 V
→
8.0 V
I
out
= 1.0 A
= Reg
line
= 2.4 mV
t, TIME (2.0 ms/DIV)
VOLTAGE (V)
VOLTAGE DEVIATION (V)
(2.0 mV/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
T
J
, JUNCTION TEMPERATURE (
°
C)
NORMALIZED OUTPUT VOLTAGE
10
0
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
= Reg
therm
= 0.0030% V
O
/W = Reg
therm
= 0.0020% V
O
/W
Z
O
Ω
, OUTPUT IMPEDANCE ( )
