Datasheet
Introduction
www.ti.com
1 Introduction
1.1 EVM Features
• Evaluation module for bq25504
• Ultra low power boost converter/charger with battery management for energy harvester applications
• Resistor-programmable settings for under voltage, over voltage providing flexible battery management;
POTs Included for fine tuning the settings (not populated)
• Programmable push-pull output Indicator for battery status (VBAT_OK)
• Test points for key signals available for testing purpose – easy probe hook-up.
• Jumpers available – easy to change settings
1.2 General Description
The bq25504 is the first of a new family of intelligent integrated energy harvesting Nano-Power
management solutions that are well suited for meeting the special needs of ultra low power applications.
The product is specifically designed to efficiently acquire and manage the microwatts (µW) to miliwatts
(mW) of power generated from a variety of DC sources like photovoltaic (solar) or thermal electric
generators. The bq25504 is the first device of its kind to implement a highly efficient boost
converter/charger targeted toward products and systems, such as wireless sensor networks (WSN) which
have stringent power and operational demands. The design of the bq25504 starts with a DC-DC boost
converter/charger that requires only microwatts of power to begin operating. Once started, the boost
converter/charger can effectively extract power from low voltage output harvesters such as thermoelectric
generators (TEGs) or single / dual cell solar panels. The boost converter can be started with VIN as low
as 330 mV typ., and once started, can continue to harvest energy down to V
IN
≃ 100 mV.
The bq25504 also implements a programmable maximum power point tracking (MPPT) sampling network
to optimize the transfer of power into the device. The MPP is listed by the harvesting manufacturer as a
percentage of its open circuit (OC) voltage. Typically solar cells are at their MPP when loaded to ~80% of
their OC voltage. The bq25504 periodically samples the open circuit input voltage by disabling the boost
converter (approximately every 16 seconds) and stores the programmed MPP ratio of the OC voltage on
the external reference capacitor, C5. If the storage element is less than the maximum voltage (OV) then
the boost converter will load the harvesting source until it reaches the MPP (C5 voltage reference) and
then regulate the input voltage of the converter, thus transferring the maximum amount of power to the
output. Alternatively, an external reference voltage can be provided, by a MCU to the REFS pin, to adjust
C5 independently. The shunt on JP1 has to be moved from the Divider setting to STOR when providing
this external reference (JP1-2 tied to JP1-1 – OSC/STOR).
The bq25504 was designed with the flexibility to support a variety of energy storage elements. The
availability of the sources from which harvesters extract their energy can often be sporadic or
time-varying. Systems will typically need some type of energy storage element, such as a re-chargeable
battery, super capacitor, or conventional capacitor. The storage element will make certain constant power
is available when needed for the systems. The storage element also allows the system to handle any peak
currents that can not directly come from the input source.
To prevent damage to a customer’s storage element, both maximum and minimum voltages are monitored
against the user programmed under-voltage (UV) and over-voltage (OV) levels.
To further assist users in the strict management of their energy budgets, the bq25504 toggles the battery
good flag to signal the microprocessor when the voltage on an energy storage element or capacitor has
dropped below a pre-set critical level. This should trigger the shedding of load currents to prevent the
system from entering an under voltage condition.
The OV, UV and battery good thresholds are programmed independently. The EVM has three 500KΩ
potentiometers (not installed at factory) to allow fine tuning of the three programmable thresholds. This
only need be done if the user needs precision, the POTs provide about ±50mV shift.
For details, see bq25504 data sheet (SLUSAH0).
2
bq25504 EVM – Ultra Low Power Boost Converter with Battery Management for SLUU654A–October 2011–Revised October 2011
Energy Harvester Applications
Submit Documentation Feedback
Copyright © 2011, Texas Instruments Incorporated