EVM Performance Specification Summary
2
EVM Performance Specification Summary
See Data Sheet “Recommended Operating Conditions” for component adjustments. For details about the
resistor programmable settings, see bq25505 data sheet (
MIN
NOM
MAX
UNIT
VIN(DC)
DC input voltage into VIN_DC
0.13
4.0
V
VIN_STARTUP(D
DC minimum start-up voltage into depleted storage element, no load attached
330
mV
C)
to VSTOR or VOUT and IBAT(LEAK)
≤
1 µA
VBAT_OV
Battery overvoltage Threshold –min and max values include ±2% set point
4.04
4.18
4.32
V
accuracy and ±1% resistor tolerance but excludes effects of output ripple
OK_HYST indication toggles high when VSTOR ramps up - min and max
2.70
2.79
2.88
V
values include ±2% set point accuracy and ±1% resistor tolerance
VBAT_OK
OK_PROG indication toggles low when VSTOR ramps down - min and max
2.89
2.99
3.09
V
values include ±2% set point accuracy and ±1% resistor tolerance
MPPT
Maximum Power Point Tracking, Resistor Programmed % of Open Circuit
80%
Voltage
CBAT
A 100-µF low leakage ceramic capacitor is installed on the EVM as the
100
µF
minimum recommended equivalent battery capacitance.
See
spreadsheet tool to assist with modifying the MPPT, VBAT_OV and VBAT_OK resistors for
your application.
CAUTION
If changing the board resistors or the capacitor on VREF_SAMP (C2), it is
important to remember that residual solder flux on a board has a resistivity in
the 1–20 M
Ω
range. Therefore, flux remaining in parallel with changed 1–20
M
Ω
resistors can result in a lower effective resistances, which will produce
different operating thresholds than expected. Similarly, flux remaining in parallel
with the VREF_SAMP capacitor provides an additional leakage path, which
results in the input voltage regulation set point drooping during the 16-s MPPT
cycle. Therefore, it is highly recommended that boards be thoroughly cleaned
twice, once after removing the old components and again after installing the
new components. If possible, the boards should be cleaned until the wash
solution measures ionic contamination greater than 50 M
Ω
.
3
Test and Measurement Summary
Test Setup Tips
Energy harvesting power sources are high impedance sources. A source-meter configured as a current
source with voltage compliance set to the harvester's open circuit voltage is the best way to simulate the
harvester. When simulating a Hi-Z energy harvester with low output impedance lab power supply, it is
necessary to simulate the harvester's impedance with a physical resistor between the supply, VPS, and
VIN_DC of the EVM. When the MPPT sampling circuit is active, VIN_DC = VPS = the harvester open
circuit voltage (VIN_OC) because there is no input current to create a drop across the simulated
impedance (that is, open circuit); therefore, VPS should be set to the intended harvester's open circuit
voltage. When the boost converter is running, it draws only enough current until the voltage at VIN_DC
droops to the MPPT's sampled voltage that is stored at VREF_SAMP.
The battery (storage element) can be replaced with a simulated battery. Often electronic 4 quadrant loads
give erratic results with a “battery charger” due to the charger changing states (fast-charge to termination
and refresh) while the electronic load is changing loads to maintain the “battery” voltage. The charging and
loading get out of phase and create a large signal oscillation which is due to the 4 quadrant meter. A
simple circuit can be used to simulate a battery and can be adjusted for voltage. It consists of load resistor
(~10
Ω
, 2 W) to pull the output down to some minimum storage voltage (sinking current part of battery)
and a lab supply connected to the BAT pin via a diode. The lab supply biases up the battery voltage to the
desired level. It may be necessary to add more capacitance across R1.
7
SLUUAA8 – September 2013
User's Guide for bq25505 Battery Charger Evaluation Module for Energy
Harvesting
Copyright © 2013, Texas Instruments Incorporated
