The bq25570 is a highly integrated energy harvesting Nano-Power management solution that is 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 milliwatts (mW) of power generated from a variety of DC sources like photovoltaic (solar) or thermal electric generators. The bq25570 is the first device of its kind to implement a highly efficient boost converter/charger with a nano-powered buck converter targeted toward products and systems, such as wireless sensor networks (WSN) which have stringent power and operational demands. The design of the bq25570 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 or dual cell solar panels. The boost converter can be started with VIN as low as 330 mV, and once started, can continue to harvest energy down to VIN = 100 mV.
The bq25570 also implements a programmable maximum power point tracking sampling network to optimize the transfer of power into the device. The fraction of open circuit voltage that is sampled and held can be controlled by pulling VOC_SAMP high or low (80% or 50% respectively) or by using external resistors. This sampled voltage is maintained via internal sampling circuitry and held with an external capacitor (CREF) on the VREF_SAMP pin. For example, solar cells typically operate with a maximum power point (MPP) of 80% of their open circuit voltage. Connecting VOC_SAMP to VSTOR sets the MPPT threshold to 80% and results in the IC regulating the voltage on the solar cell to ensure that the VIN_DC voltage does not fail below the voltage on CREF which equals 80% of the solar panel’s open circuit voltage. Alternatively, an external reference voltage can be provided by a MCU to produce a more complex MPPT algorithm. In addition to the boost charging front end, the bq25570 provides the system with an externally programmable regulated supply via the buck converter. The regulated output has been optimized to provide high efficiency across low output currents (< 10 μA) to high currents (~110 mA).
The bq25570 is 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 internally set under-voltage (UV) and user programmable over-voltage (OV) levels.
To further assist users in the strict management of their energy budgets, the bq25570 toggles the battery good (VBAT_OK) 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 reduction of load currents to prevent the system from entering an under voltage condition. There is also independent enable signals to allow the system to control when to run the regulated output or even put the whole IC into an ultra-low quiescent current sleep state.All the capabilities of bq25570 are packed into a small foot-print 20-lead 3.5mm x 3.5 mm QFN package (RGR).
bq25570主要特性:
Programmable input voltage regulation setting via jumpers or resistors
Programmable charger output voltage maximum setting via resistors (currently 4.2V)
Programmable charger output voltage maximum setting via resistors (currently 1.8V)
Programmable power good (BAT_OK) voltage setting via resistors (currently 3.0V)
Multiple jumpers, connectors and test points availabl
bq25570应用:
• Battery Charging and Protection
• Energy Harvesting
• Solar Charger
• Thermal Electric Generator (TEG) Harvesting
• Wireless Sensor Networks (WSN)
• Low Power Wireless Monitoring
• Environmental Monitoring
• Bridge and Structural Health Monitoring (SHM)
• Smart Building Controls
• Portable and Wearable Health Device
• Entertainment System Remote Controls
图1. bq25570框图
This user’s guide describes the bq25570 evaluation module (EVM), how to perform a stand-alone
evaluation and how to allow the EVM to interface with the system and host. The boost converter output has been configured to deliver up to 4.2-V maximum voltage to its output, VSTOR, using external resistors. This voltage will be applied to the storage element as long as the storage element voltage at VBAT is above the internally programmed undervoltage of 2.0 V. The integrated buck converter provides up to 1.8 V and 100 mA at VOUT. The VBAT_OK indicator toggles high when VSTOR ramps up to 3.0 V and toggles low when VSTOR ramps down to 2.8 V.
The bq25570 is an integrated energy harvesting Nano-Power management solution that is 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 high output impedance (HiZ) DC sources like photovoltaic (solar) or thermal electric generators; or with an AC/DC rectifier, a piezoelectric generator. The bq25570 implements a highly efficient, pulse-frequency modulated (PFM) boost converter/charger targeted toward products and systems, such as wireless sensor networks (WSN) which have stringent power and operational demands. Assuming a depleted storage element has been attached, the bq25570 DC-DC boost converter/charger that requires only microwatts of power to begin operating in cold start mode. Once the boost converter output, VSTOR, reaches ~1.8 V and can now power the converter, the main boost converter can now more efficiently extract power from low voltage output harvesters such as thermoelectric generators (TEGs) or single and dual cell solar panels. For example, assuming the HiZ input source can provide at least 5 μW typical and the load on VSTOR (including the storage element leakage current) is less than 1 μA of leakage current, the boost converter can be started with VIN_DC as low as 330 mV typ., and once VSTOR reaches 1.8 V, can continue to harvest energy down to VIN_DC ≃ 120 mV. The integrated PFM buck converter is also powered from VSTOR and, assuming enough input power is available, provides up to 100 mA from the VOUT pin. The VOUT voltage is externally programmed to slightly less than the VSTOR voltage.
HiZ DC sources have a maximum output power point (MPP) that varies with ambient conditions. For example, a solar panel’s MPP varies with the amount of light on the panel and with temperature. The MPP is listed by the harvesting source manufacturer as a percentage of its open circuit (OC) voltage. Therefore, the bq25570 implements a programmable maximum power point tracking (MPPT) sampling network to optimize the transfer of power into the device. The bq25570 periodically samples the open circuit input voltage every 16 seconds by disabling the boost converter for 256 ms and stores the programmed MPP ratio of the OC voltage on the external reference capacitor (C2) at VREF_SAMP. Typically solar cells are at their MPP when loaded to ~70–80% of their OC voltage and TEGs at ~50%. While the storage element is less than the user programmed maximum voltage (VBAT_OV), the boost converter loads the harvesting source until VIN_DC reaches the MPP (voltage at VREF_SAMP). This results in the boost converter regulating the input voltage of the converter until the output reaches VBAT_OV, thus transferring the maximum amount of power currently available per ambient conditions to the output.
The battery undervoltage, VBAT_UV, threshold is checked continuously to ensure that the internal battery FET, connecting VSTOR to VBAT, does not turn on until VSTOR is above the VBAT_UV threshold (2.0 V).The over voltage (VBAT_OV) setting initially is lower than the programmed value at startup (varies on conditions) and is updated after the first ~32 ms. Subsequent updates are every ~64 ms. The VBAT_OV
threshold sets maximum voltage on VSTOR and the boost converter stops switching when the voltage on VSTOR reaches the VBAT_OV threshold. The open circuit input voltage (VIN_OC) is measured every ~16 seconds in order for the Maximum Power Point Tracking (MPPT) circuit to sample and hold the input regulation voltage. This periodic update continually optimizes maximum power delivery based on the harvesting conditions.
The bq25570 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 timevarying. 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. In general, the storage element also allows the system to handle any peak currents that can not directly come from the input source. It is important to remember that batteries and super capacitors can have significant leakage currents that need to be included with determining the loading on VSTOR.
To prevent damage to a customer’s storage element, both maximum and minimum voltages are monitored against the internally programmed under-voltage (VBAT_UV) and user programmed over-voltage (VBAT_OV) levels.
To further assist users in the strict management of their energy budgets, the bq25570 toggles a user programmable battery good flag (VBAT_OK), checked every 64 ms, to signal the microprocessor when the voltage on an energy storage element or capacitor has risen above (OK_HYST threshold) or dropped below (OK_PROG threshold) a pre-set critical level. To prevent the system from entering an undervoltage condition or if starting up into a depleted storage element, it is highly recommended to isolate the system load from VSTOR by 1) setting VBAT_OK equal to the buck converter’s enable signal VOUT_EN and 2) using an NFET to invert the BAT_OK signal so that it drives the gate of PFET, which isolates the system load from VSTOR.
bq25570 电池充电评估模块(EVM)主要特性:
• Evaluation module for bq25570
• Ultra-low power boost converter/charger and buck converter with battery management for energy harvester applications
• Resistor-programmable settings for under voltage, over voltage providing flexible battery management
• 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
举报
