UG-439
Evaluation Board User Guide
Rev. A | Page 6 of 13
Measuring Efficiency of the Buck Regulator
Measure the efficiency, η, by comparing the input power with
the output power.
IN
IN
OUT
OUT
I
V
I
V
η
×
×
=
Measure the input and output voltages as close as possible to the
input and output capacitors to reduce the effect of IR drops.
The buck regulator efficiency plots for V
OUT2
= 3.3 V and V
OUT2
=
1.8 V are shown in Figure 11 and Figure 12, respectively.
Figure 11. Buck Regulator Efficiency, V
IN2
= 4.2 V, V
OUT2
= 3.3 V
Figure 12. Buck Regulator Efficiency, V
IN2
= 3.6 V, V
OUT2
= 1.8 V
Measuring Inductor Current
Measure the inductor current by removing one end of the inductor
from its pad and connecting a current loop in series. Connect a
current probe to this wire.
Measuring Line Regulation of LDO Regulators
For line regulation measurements, the output of the regulator
is monitored while its input is varied. For optimal line regula-
tion, 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
n 0.5 V
(or 2.3 V, whichever is greater) and V
IN
maximum. For example,
a fixed 3.3 V output needs V
IN
to be varied between 3.8 V and
5.5 V. This measurement can be repeated under different load
conditions. Figure 13 shows the typical line regulation performance
of the LDO regulator with a fixed 3.3 V output.
Figure 13. V
OUT
vs. V
IN
, LDO Line Regulation for an Output of 3.3 V
Measuring Load Regulation of LDO Regulators
For load regulation measurements, the regulator output is
monitored while the load is varied. For optimal load regulation,
the output must change as little as possible with varying loads.
The input voltage must be held constant during this measurement.
The load current can be varied from 0 mA to 300 mA. Figure 14
shows the typical load regulation performance of the LDO
regulator with a 3.3 V output for different input voltages.
Figure 14. V
OUT
vs. I
LOAD
, LDO Load Regulation
0
10
20
30
40
50
60
70
80
90
100
1
10
100
1000
10000
E
FFIC
IE
N
C
Y
(
%)
I
LOAD
(mA)
PSM MODE
PWM MODE
10895-
212
100
0
1
10
100
1k
10k
E
F
F
ICI
E
NCY
(
%)
I
LOAD
(mA)
10
20
30
40
50
60
70
80
90
PSM
PWM
10895-
1
10
3.317
3.311
3.6
4.1
4.6
5.6
5.1
V
O
UT
(V)
V
IN
(V)
3.312
3.313
3.314
3.315
3.316
10895-
010
I
LOAD
= 1mA
I
LOAD
= 10mA
I
LOAD
= 100mA
I
LOAD
= 200mA
I
LOAD
= 300mA
3.3160
3.3110
0
300
250
200
150
100
50
V
O
UT
(V)
I
LOAD
(mA)
3.3115
3.3120
3.3125
3.3130
3.3135
3.3140
3.3145
3.3150
3.3155
10895-
0
1
1
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5.5V
