4
AN1386.1
December 23, 2009
Efficiency and Output
Ripple/Noise Measurement
Figure 5 shows the efficiency measurement schematic for
the ISL820xMEVAL1Z POL module. The voltage and
current meter can be used to measure input/output
voltage and current. In order to obtain an accurate
measurement and prevent the voltage drop of PCB or
wire trace, the voltage meter must be close to the
input/output pin of the POL module.
The efficiency equation is shown in Equation 1:
The equipment setup for the efficiency measurement on
the evaluation board is shown in Figure 6. The measuring
point for the input voltage meter is at the C
3
terminal,
and the measuring point for the output voltage meter is
at the C
8
terminal (refer to Figure 9).
Output Ripple/Noise Measurement Method
The total noise is equal to the sum of the ripple and
noise components. Simple steps should be taken to
assure that there is minimum pickup noise due to the
high frequency events, which can be magnified by the
large ground loop formed by the oscilloscope probe
ground. This means that even a few inches of ground
wire on the oscilloscope probe may result in hundreds of
millivolts of noise spikes when improperly routed or
terminated. This effect can be overcome by using the
short loop measurement method to minimize the
measurement loop area for reducing the pickup noise.
The short loop measurement method is shown in
Figure 7. For ISL820xMEVAL1Z evaluation board, the
output ripple/noise measurement point is located at the
C
8
terminal (refer to Figure 9).
Efficiency
Output Power
Input Power
------------------------------------
P
OUT
P
IN
----------------
V
OUT
I
OUT
•
(
)
V
IN
I
IN
•
(
)
----------------------------------------
=
=
=
(EQ. 1)
FIGURE 5. EFFICIENCY MEASUREMENT SCHEMATIC
PVCC
VIN
VOUT
Cin
Cout
R
FB
R
SEN-EX
C
PVCC
+
-
DC Source
DC Load
Vi
Ai
Vo
+
-
DC Source
Iin
Vin
Vout
Iout
PGND
FB
COMP/EN
VIN
VOUT
PHASE
ISET
PVCC
ELECTRONIC LOAD
Vin
DC POWER SUPPLY
PVCC
DC POWER SUPPLY
Current
Meter
Voltage
Meter
Voltage
Meter
+
-
+
-
FIGURE 6. EQUIPMENT SETUP FOR EFFICIENCY
MEASUREMENT
SHORT LOOP
MEASUREMENT
METHOD
FIGURE 7. OUTPUT RIPPLE/NOISE
MEASUREMENT METHOD
Application Note 1386
