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BQ25504 View Datasheet(PDF) - Texas Instruments

Part NameDescriptionManufacturer
BQ25504 Ultra Low-Power Boost Converter With Battery Management for Energy Harvester Applications Texas-Instruments
Texas Instruments Texas-Instruments
BQ25504 Datasheet PDF : 36 Pages
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bq25504
SLUSAH0C – OCTOBER 2011 – REVISED JUNE 2015
8.2 Functional Block Diagram
LBST
VSTOR
VBAT
VSS
www.ti.com
VSS
VIN_DC
Cold-Start
Unit
Enable
Interrupt
Boost Charge
Controller
Enable
VOC_SAMP
VREF_SAMP
MPPT
Controller
BAT_SAVE
Vref
OT
Temperature
Sensing
Element
Bias Reference
and Oscillator
Vref
Battery Threshold
Control
OK
Vref
AVSS
VBAT_OK
OK_PROG
OK_HYST
OT_PROG VBAT_OV VRDIV VBAT_UV
8.3 Feature Description
8.3.1 Maximum Power Point Tracking
Maximum power point tracking (MPPT) is implemented in order to maximize the power extracted from an energy
harvester source. The boost converter indirectly modulates the input impedance of the main boost charger by
regulating the charger's input voltage, as sensed by the VIN_DC pin, to the sampled reference voltage stored on
the VREF_SAMP pin. The MPPT circuit obtains a new reference voltage every 16 s (typical) by periodically
disabling the charger for 256 ms (typical) and sampling a fraction of the harvester's open-circuit voltage (VOC).
For solar harvesters, the maximum power point is typically 70%-80% of VOC and for thermoelectric harvesters,
the MPPT is typically 50%. The exact ratio for MPPT can be optimized to meet the needs of the input source
being used by connecting external resistors ROC1 and ROC2 between VIN_DC and GND with mid-point at
VOC_SAMP.
æ
VREF_SAMP = VIN_DC(OpenCircuit)ç
ROC1
ö
÷
è ROC1 + ROC2 ø
(1)
Spreadsheet SLUC484 provides help on sizing and selecting the resistors.
10
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