bq25505 PMICs with Boost Charger and Autonomous Power Multiplexor
Created: Jun 13, 2016
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The energy garnering devices are widely used today to aid application of renewable energy and to enhance the system efficiency. The reference design is an evaluation board from TI which features bq25505 an integrated energy harvesting nano-power management solution that is well suited for meeting the special needs of low power applications designed to efficiently extract microwatts (µW) to milliwatts (mW) to power generated from a variety of DC energy harvesting. The reference design is a solution for power management system, which features autonomous selection of battery storage and boost charging process.
The reference design can gather power from different low voltage output harvesters such as Thermoelectric Generators (TEGs) or single- and dual-cell solar panels. With different output harvesters, Maximum Power Point (MPP) varies with ambient conditions. Thus, bq25505 implements a programmable Maximum Power Point Tracking (MPPT) sampling network to optimize the transfer of power into the device, where MPP is a percentage of Open Circuit (OC). The bq25505 periodically samples the open circuit input voltage every 16s by disabling the boost converter for 256ms and stores the programmed MPP ratio of the OC voltage on the external reference capacitor (C2) at VREF_SAMP. When the storage element is less than the user programmed maximum voltage (VBAT_OV), the boost converter helps the storage element by loading the harvesting source until the VIN_DC reaches the MPP or the voltage at the VREF_SAMP. The battery undervoltage VBAT_UV is continuously check to ensure that the internal battery FET, connecting VSTOR to VBAT_SEC, will just turn on when the VSTOR (connection to the load) is above the VBAT_UV threshold (2V). The overvoltage (VBAT_OV) is initially set lower than the programmed value at startup and updated after the first ~ 32ms, thus following updates are every ~64ms. The integrated multiplexer gate drivers in the bq25505 autonomously switch the systems load to the primary non-rechargeable storage if the secondary rechargeable battery is depleted and below the voltage of the user-defined VBAT_OK threshold.
The bq25505 application can be found on bridge and structural health monitoring (SHM), environmental monitoring, Wireless Sensor Networks (WSN), thermal electric generator (TEG) harvesting, and entertainment system remote controls.