2-cell Li-Ion linear charger in SOIC-8
The Texas Instruments BQ2057WSNTRG4 is a linear charge-management IC designed for 2-cell Lithium Ion/Polymer battery packs, regulating the float voltage to 8.4V. It delivers a constant charging current that is programmable via an external resistor, suiting it for portable equipment, handheld instruments, and battery-backed systems where a simple, low-noise charging solution is preferred over a switching regulator.
Charge current and voltage setpoints
The 2-cell configuration sets the regulated battery pack voltage at 8.4V, which is the standard termination voltage for a series stack of two Li-Ion or Li-Polymer cells. The charge current is constant and programmable, meaning the designer selects an external sense resistor to set the rate — typically between C/10 and 1C depending on the cell capacity and thermal budget. Maximum supply voltage is 15V, so the input rail should be a regulated 9V to 12V DC source — unregulated wall adapters that sag under load can cause premature termination.
Package and footprint reality
The Tape & Reel (TR) suffix indicates it ships on 13-inch reels, which is the standard format for automated pick-and-place assembly lines. The 8-SOIC package has a moderate thermal impedance — for charge currents above 500 mA, the PCB copper area under the IC should be maximised to keep the junction temperature within the -20°C to 70°C operating envelope.