40
50
60
70
80
90
100
0.001
0.01
0.1
1
10
100
E
ff
ici
e
n
cy
(
%
)
Output Current (mA)
VSTOR = 2.1V
VSTOR = 3.6V
VSTOR = 5.5V
VOUT = 1.8V, TA = 25
o
C
+ VM1 -
-
VM2
+
+ CM2 -
+ PS1 -
+
CM1
-
Test and Measurment Summary
Figure 5. Test Setup for Measuring Buck Converter Efficiency
Figure 6. Buck Converter Efficiency versus Output Current
The buck converter is powered from VSTOR; therefore, to measure its efficiency alone, VIN_DC should
be left floating, and the input power supply applied to VSTOR. To filter bursts of current due to PFM
switching, the series input current meter from the VSTOR supply must be set to the highest level of
filtering and/or averaging, which will result in longer than usual measurement times.
Alternatively, these measurements can be taken with source-meters instead of discrete power supply,
resistor load box and meters. The source-meter on VSTOR is configured as a voltage source. The source-
meter on OUT can be configured as either a current source that sinks current (i.e., negative current) or as
a voltage source with voltage at least 100 mV below the lowest expected regulation voltage point.
11
SLUUAA7A – July 2013 – Revised August 2014
User's Guide for bq25570 Battery Charger Evaluation Module for Energy
Harvesting
Copyright © 2013–2014, Texas Instruments Incorporated
