I²C-controlled, 18-V max input 2-A single-cell battery charger with USB detection and ADC

The BQ25628

and BQ25629 are highly-integrated 2A switch-mode battery charge management and system

power path management devices for single cell Li-ion and Li-polymer batteries. The solution

is highly integrated with built-in current sensing, loop compensation, input

reverse-blocking FET (RBFET, Q1), high-side switching FET (HSFET, Q2), low-side switching

FET (LSFET, Q3), and battery FET (BATFET, Q4) between system and battery. The device uses

narrow VDC power path management, regulating the system slightly above the battery voltage

without dropping below a configurable minimum system voltage. The low impedance power path

optimizes switch-mode operation efficiency, reduces battery charging time, extends battery

life during discharging phase, and the ultra-low 0.15µA ship mode current extends battery

shelf life. The I2C serial interface with charging and system settings makes BQ25628

and BQ25629 truly flexible solutions.

The BQ25628 has the ILIM pin to set the

default input current limit and TSBIAS pin for controlled thermistor bias. The BQ25629

supports a wide range of input sources, including standard USB host port and USB charging

port. The device is compliant with USB 2.0 and USB 3.0 power specifications for input

current and voltage regulation and meets the USB On-the-Go (OTG) operation power rating

specification up to 2.0A.

The power path management regulates the

system slightly above battery voltage but does not drop below the programmable minimum

system voltage. With this feature, the system maintains operation even when the battery is

completely depleted or removed. When the input current limit or input voltage limit is

reached, the power path management automatically reduces the charge current. As the system

load continues to increase, the battery starts to discharge until the system power

requirement is met. This supplement mode prevents overloading the input source.

The BQ25628

and BQ25629 power an accessory attached to PMID either directly from the adapter or from the

battery in either boost or bypass OTG modes. Boost OTG provides a regulated voltage at PMID

from the battery via boost operation in the converter. Bypass OTG provides a direct path

from the battery to PMID for highest efficiency. The BQ25628 and BQ25629 may be configured

to automatically transition into boost OTG mode when the adapter is removed, and back into

forward charging when the adapter is attached in order to power PMID in either configuration

without host intervention. In forward charging, boost OTG and bypass OTG, the PMIDGD signal

indicates PMID voltage and current are within accepted ranges. PMIDGD may be used to drive

an external PMOS FET to protect attached accessories by disconnecting them from PMID if an

out-of-range voltage or current is detected.

The BQ25628

and BQ25629 initiate and complete a charging cycle

without host control. By sensing the battery voltage, it charges the battery in four

different phases: trickle charge, pre-charge, constant current (CC) charge and constant

voltage (CV) charge. At the end of the charging cycle, the charger automatically terminates

when the charge current is below a preset threshold and the battery voltage is higher than

the recharge threshold. Termination is supported for all TS pin temperature zones.

The BQ25628

and BQ25629 provide various safety features for

battery charging and system operations, including battery negative temperature coefficient

thermistor monitoring, charging safety timer and overvoltage and overcurrent protections.

The thermal regulation reduces charge current when the junction temperature exceeds the

programmable threshold. The STAT output reports the charging status and any fault

conditions. Other safety features include battery temperature sensing for charge mode and

OTG boost mode, thermal shutdown and input UVLO and overvoltage protection. The

INT output notifies the host when a fault occurs or status

changes.

The BQ25628

and BQ25629 are available in a 18-pin, 2.5mm × 3.0mm

WQFN package.