BQ25504 Datasheet, PDF (17/24 Pages) Texas Instruments – Ultra Low Power Boost Converter with Battery Management for Energy Harvester Applications

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bq25504
SLUSAH0 – OCTOBER 2011
Storage capacitor:
An additional storage capacitor CBAT, either stand-alone, or in parallel with the battery should be attached
between Pin 14 (VBAT) and GND. The value of this capacitor should be selected to meet the needs of any load
attached to the battery. For instance, some Li-ion batteries or thin-film batteries may not have the current
capacity to meet the surge current requirements of an attached low power radio. Therefore, adding a capacitor
may help buffer this load and provide the brief current surge needs.
Additionally, when the system load has large transients, adding a small high frequency capacitor in parallel to
C_STOR may help buffer this load and provide the brief current surge needs.
For a recommend list of standard components, please see the EVM User’s guide.
LAYOUT CONSIDERATIONS
As for all switching power supplies, the layout is an important step in the design, especially at high peak currents
and high switching frequencies. If the layout is not carefully done, the boost converter/charger could show
stability problems as well as EMI problems. Therefore, use wide and short traces for the main current path and
for the power ground paths. The input and output capacitor, as well as the inductor should be placed as close as
possible to the IC.
The resistors that program the thresholds should be placed as close as possible to the input pins of the IC to
minimize parasitic capacitance to less than 2 pF.
To layout the ground, it is recommended to use short traces as well, separated from the power ground traces.
This avoids ground shift problems, which can occur due to superimposition of power ground current and control
ground current. Assure that the ground traces are connected close to the device GND pin.
THERMAL CONSIDERATIONS
Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires
special attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, added
heat sinks and convection surfaces, and the presence of other heat-generating components affect the
power-dissipation limits of a given component.
Three basic approaches for enhancing thermal performance are listed below.
• Improving the power-dissipation capability of the PCB design
• Improving the thermal coupling of the component to the PCB
• Introducing airflow in the system
For more details on how to use the thermal parameters in the Thermal Table, check the Thermal Characteristics
Application Note (SZZA017) and the IC Package Thermal Metrics Application Note (SPRA953).
Copyright © 2011, Texas Instruments Incorporated
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