UG-279 Evaluation Board User Guide
Rev. 0 | Page 4 of 12
Measuring Load Regulation
Test the load regulation by increasing the load at the output
and looking at the change in output voltage. To minimize
voltage drop, use short low resistance wires, especially for loads
approaching maximum current.
3.295
3.300
3.305
3.310
3.315
3.320
3.325
0 0.10.20.30.40.50.60.7
V
OUT
(V)
I
OUT
(A)
V
IN
= 5V
V
OUT
= 3.3V
09879-002
Figure 2. Buck Load Regulation
Measuring Line Regulation
Vary the input voltage and examine the change in the output
voltage.
1.790
1.795
1.800
1.805
1.810
4.54.74.95.15.35.5
V
OUT
(V)
V
IN
(V)
V
IN
= 5V
V
OUT
= 1.8V
LOAD = 500mA
09879-003
Figure 3. Buck Line Regulation
Measuring Efficiency
Measure the efficiency, η, by comparing the input power with
the output power.
ININ
OUTOUT
IV
IV
η
×
×
=
Measure the input and output voltages as close as possible to the
input and output capacitors to reduce the effect of IR drops.
0
10
20
30
40
50
60
70
80
90
100
110100
EFFICIENCY (%)
I
OUT
(mA)
1000
PSM
PWM
V
IN
= 5V
V
OUT
= 3.3V
09879-004
Figure 4. Buck Efficiency
Measuring Inductor Current
Measure the inductor current by removing one end of the
inductor from its pad and connecting a current loop in series.
A current probe can be connected onto this wire.
Line Regulation of LDOs
For line regulation measurements, the regulator output is
monitored while its input is varied. For good line regulation,
the output must change as little as possible with varying input
levels. To ensure that the device is not in dropout mode during
this measurement, V
IN
must be varied between V
OUT
nominal
+ 0.5 V (or 2.3 V, whichever is greater) and V
IN
maximum. For
example, a fixed 2.8 V output needs V
IN
to be varied between
3.3 V and 5.5 V. This measurement can be repeated under
different load conditions. Figure 5 shows the typical line
regulation performance of the LDO with fixed 2.8 V output.
2.780
2.785
2.790
2.795
2.800
2.805
3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
V
IN
(V)
V
OUT
(V)
I
OUT
= 150mA
I
OUT
= 100mA
I
OUT
= 10mA
I
OUT
= 1mA
I
OUT
= 100µA
09879-005
Figure 5. LDO Line Regulation
