bq25570

SLUSBH2C – MARCH 2013 – REVISED JANUARY 2014

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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

DESCRIPTION CONTINUED

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).

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