Texas Instruments bq25505, Руководство пользователя

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100
0.01 0.1 1 10 100
E
ff
ici
e
n
cy
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%
)
Input Current (mA)
VSTOR = 1.8 V
VSTOR = 3.0 V
VSTOR = 5.5 V
VIN = 0.5 V
0
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E
ff
ici
e
n
cy
(
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Input Voltage (V)
VSTOR = 2.0 V
VSTOR = 3.0 V
VSTOR = 5.5 V
IIN = 100
P
A
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Test and Measurement Summary
Figure 3. Charger Efficiency versus Input Voltage
Figure 4. Charger Efficiency versus Input Current
Because the boost converter regulates input voltage instead of output voltage, uses PFM switching,
operates at very low currents, and has MPPT, efficiency cannot be measured using the same test setup
as for an output regulating, higher power, fixed-frequency PWM switching boost converter. The VSTOR
output must be held at a fixed voltage (below VBAT_OV threshold) by an external source that is capable
of sinking current, with that sunk current being the measured output current. In addition to filtering bursts
of current due to PFM switching and the ripple voltage on VIN_DC due to input voltage regulation, the
series input current meter and input voltage meter must be set to filtering/averaging which will result in
longer than usual measurement times, but not longer than the 16-s MPPT sample time. Measurements for
both VIN and IN will be most accurate when taken at the midpoint of the 16-s MPPT period. Remote
sensing by the source-meters is possible but, on the input side, the source-meter output regulation loop
and the charger MPPT input regulation loop may interfere with each other and cause the input voltage to
oscillate. Adding a large capacitor across VIN_DC and GND will eliminate this oscillation but the
capacitor's leakage current will inflate the input current measurement and result in lower efficiency.
See SLUA691 for a detailed explanation on how to take these and other measurements with source-
meters.
3.1.2 Boost Charger Operation during Battery Charging
The test setup is shown in Figure 5 . The specific equipment used for the test results in Figure 6 is listed
below:
1. VIN_DC and VBAT_SEC are configured as shown in Section 3.1.2 .
2. The boost charger inductor current (IL) was measured by using an oscilloscope current probe across a
current loop that was inserted in series with inductor L1.
9 SLUUAA8 – September 2013 User's Guide for bq25505 Battery Charger Evaluation Module for Energy
Harvesting
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