Nothing frustrates a cell phone user more than a dead battery. Swapping out batteries is an increasingly rare option, so fast charging is the order of the day. However it takes a well designed charge-management IC to quickly charge a large cell phone battery without causing it to overheat or expire prematurely.
Renesas has introduced a Lithium-Ion battery charge IC with support for large-current rapid charging. The R2A20057BM integrates a 2 MHz step-down DC-DC converter and supports 2A large-current charging in a 2.47 mm × 2.47 mm 25-pin WL-BGA package. Wafer-level packaging and 90% efficiency means the new chips can replace multiple power MOSFETs with large heatsinks. I could fit 16 of these tiny chips on my thumbnail, though I can’t vouch for its thermal conductivity.
On the input side the 25V high input-voltage tolerance enables a built-in overvoltage protection circuit, eliminating the need such external circuitry.
On the output side the R2A20057BM automatically identifies six USB port types, including the three types stipulated in the USB Battery Charging Specification, Revision 1.2, and sets the input current limit value automatically. The charge voltage is prevision controlled at 4.2V or 4.35V ± 0.5%. The input current limitation is programmable via I2C or an external control signal (CTL and USUP).
When your cell phone battery goes dead you may want to continue to use your phone while it charges. The R2A20057BM has a dual-output control circuit with a built-in load current distribution function that prioritizes supply of power to the system and adjusts the charging current when the input current is limited.
If your battery gets low either the trickle charge or fast charge kicks in, depending on how low it is; this process is initiated when VBAT drops below Vsysswoff, the low-battery detection voltage. When VBAT > Vsysswon ( Vsysswoff + Vsysswoff_hys) , the USB detection is done and DP and DM terminals become Hi-Z (open). If, however, after 40 minutes VBAT is still lower than Vsysswoff then the R2A20057BM shifts into suspend mode—your battery is shot.
The built-in protection functions ensure safe charging by providing input/output overvoltage protection, thermal protection, charge timer protection, and thermistor-based battery temperature monitoring.
All told the R2A20057BM is a very capable charge control IC in a very small package. It’s sampling now at $4.40/unit, with production to begin in January.