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IC manufacturers Texas Instruments

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Texas Instruments BQ25505

Ultra Low Power Boost Charger with Battery Management and Autonomous Power Multiplexor for Primary Battery in Energy Harvester Applications


TopologyBoost Converter
Input voltage2-5.5 V
Output 15.5 V
IC revisionD


The bq25505 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 isspecifically 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 (TEGs). The bq25505 is a highly efficient boost charger targeted toward products and systems, such as wireless sensor networks (WSN) which have stringent power and operational demands. The design of the bq25505 starts with a DCDC boost charger that requires only microwatts of power to begin operating.Once started, the boost charger can effectively extract power from low voltage output harvesters such as TEGs or single or dual cell solar panels. The boost charger can be started with VIN as low as 330 mV, and oncestarted, can continue to harvest energy down to VIN = 120 mV.The bq25505 implements a programmable maximum power point tracking (MPPT) sampling network to optimize the transfer of power into the device. Sampling of the VIN_DC open circuit voltage is programmed using externalresistors, and that sample voltage is held with an external capacitor. For example solar cells that operate at maximum power point (MPP) of 80% of their open circuit voltage, the resistor divider can be set to 80% of theVIN_DC voltage and the network will control the VIN_DC to operate near that sampled reference voltage. Alternatively, an external reference voltage can be provide by a MCU to produce a more complex MPPT algorithm.The bq25505 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 willtypically 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 the storage element, both maximum and minimum voltages are monitored against the internally programmed undervoltage (UV) and user programmable overvoltage (OV) levels.To further assist users in the strict management of their energy budgets, the bq25505 toggles the battery good flag to signal an attached microprocessor when the voltage on an energy storage battery 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 undervoltage condition. The OV and battery good thresholds are programmed independently.In addition to the boost charging front end, bq25505 provides the system with an autonomous power multiplexor gate drive. The gate drivers allow two storage elements to be multiplexed autonomously in order to provide asingle power rail to the system load. This multiplexor is based off the VBAT_OK threshold which is resistor programmable by the user. This allows the user to set the level when the system is powered by the energy harvester storage element, e.g. rechargable battery or super capacitor or a primary non-rechargeable battery (e.g. two AA batteries). This type of hybrid system architecture allows for the run-time of a typical battery powered systems to be extended based on the amount of energy available from the harvester. If there is not sufficient energy to run the system due to extended "dark time", the primary battery is autonomously switched to the main system rail within 8 µsec in order to provide uninterrupted operation.All the capabilities of bq25505 are packed into a small foot-print 20-lead 3.5 mm x 3.5 mm QFN package.


  • Ultra Low Power With High Efficiency DC/DC Boost Charger
  • Cold-Start Voltage: VIN =330 mV
  • Continuous Energy Harvesting From Input Sources as low as 120 mV
  • Ultra Low Quiescent Current of 325 nA
  • Input Voltage Regulation Prevents Collapsing High Impedance Input Sources
  • Ship Mode with < 5 nA From Battery
  • Energy Storage
  • Energy can be Stored to Re-Chargeable Li-ion Batteries, Thin-film Batteries, Super
  • Capacitors, or Conventional Capacitors
  • Battery Charging and Protection
  • Internally Set Undervoltage Level
  • User Programmable Overvoltage Level
  • Battery Good Output Flag
  • Programmable Threshold and Hysteresis
  • Warn Attached Microcontrollers of Pending Loss of Power
  • Can be Used to Enable/Disable System Loads
  • Programmable Maximum Power Point Tracking (MPPT)
  • Integrated MPPT for optimal energy extraction from a variety of energy harvesters
  • Gate Drivers for Primary (Non-rechargeable) and Secondary (rechargeable) Storage Element Multiplexing
  • Autonomous switching based on VBAT_OK
  • Break-before-make prevents system rail droop

Typical applications

  • Smart Building Controls
  • Thermal Electric Generator (TEG) Harvesting
  • Portable and Wearable Health Devices
  • Energy Harvesting
  • Wireless Sensor Networks (WSN)
  • Industrial Monitoring
  • Environmental Monitoring
  • Solar Charger
  • Bridge and Structural Health Monitoring (SHM)
  • Entertainment System Remote Controls