USB-powered battery charger goes faster, cooler, safer
By Margery Conner, Technical Editor -- EDN, July 21, 2008
The ubiquitous USB port is becoming an international power-source standard for consumer electronics because it eliminates concerns over differences in regional wall plugs, voltages, and frequencies. Targeting that market, Texas Instruments recently introduced its bq24150 USB switch-mode battery-charge-management IC. The device couples high power-conversion efficiency with fast charging and a reverse-boost USB OTG (On-The-Go) mode that generates a voltage supply to power accessories you plug into a mini-USB port, eliminating the need for another discrete device.
By adding a tiny, 1-μH inductor and small ceramic capacitors to the 3-MHz charger, which integrates 1.25A FETs, the charging circuit fits into 7.6×10.4 mm of PCB (printed-circuit-board) space. The device can achieve peak efficiency as high as 92% and supports a USB-battery-charging current as high as 900 mA. This current speeds the charging rate without exceeding the 2.5W that the USB standard allows. The chip can handle an absolute-maximum input voltage of 20V and a maximum operating voltage of 6V, and it provides ±5% input-current-limit accuracy and ±0.5% voltage-regulation accuracy. You set the charge parameters using an I2C (interintegrated-circuit) communication interface. The chip features a safety timer with reset control and short-circuit, overvoltage, and thermal protection. The bq24150 charger comes in a 20-ball, 2×2-mm chip-scale package and sells for $2 (1000).
