FROM EDN EUROPE: Fast-charge Li-ion cells from USB
By Graham Prophet, Editor -- EDN, May 11, 2006
Summit Microelectronics' SMB 135 is a power-control chip designed for charging the higher capacity lithium-ion batteries used in today's portable applications drawing the power available from a USB port. Summit based the device on a switching-buck-regulator topology with comprehensive logic control, that accepts 4.35 to 6.0V input.
Users can program, via a graphical configuration routine that Summit provides, a complete charging algorithm. This begins with a pre-charge phase to condition a cell that is in a deep-discharge state. Next comes a high-current rapid-charge phase in which the chip can output 750 mA to the battery (while operating within the 500 mA the USB port permits), and ends with a reduction to a charge-maintenance float voltage if required. If you supply power from an AC adapter, the maximum current rises to 1A. The 135 requires a separate USB controller chip: Later devices will integrate this function.
The programming algorithm resides in EEPROM, and you load it via an I2C port. You can provide the output file from the development program to Summit , who will supply programmed parts ready-to-use. There is also a "dynamic" mode of operation which requires user programming but allows adjustments for minor differences in battery chemistries. The chip represents, the company says, the optimum use of the 500 mA available from the USB port for this purpose: the chip costs $0.98 (10,000) and comes in a 1.3×2.1-mm package.
