The bqTINY III series of devices are highly integrated Li-ion linear chargers and system power-path management devices targeted at space-limited portable applications. The bqTINY III series offer integrated USB-port and dc supply (AC adapter), power-path management with autonomous power-source selection, power FETs and current sensors, high accuracy current and voltage regulation, charge status, and charge termination in a single monolithic device.
The bqTINY III series powers the system while independently charging the battery. This feature reduces the charge and discharge cycles on the battery, allows for proper charge termination, and allows the system to run with an absent or defective battery pack. This feature also allows for the system to instantaneously turn on from an external power source in the case of a deeply discharged battery pack. The IC design is focused on supplying continuous power to the system when available from the AC, USB, or battery sources.
The power select pin (PSEL) defines which input source is to be used first (primary source is either AC or USB). If the primary source is not available, then the IC automatically switches over to the secondary source (if available) or the battery as the last option. If the PSEL is set low, the USB input is selected first and (if not available) the AC line is selected (if available) but programmed to a USB input limiting rate (100 mA/500 mA max). This feature allows the use of one input connector, where the host programs the PSEL pin according to what source is connected (AC adapter or USB port).
The ISET1 pin programs the battery's fast-charge constant current level with a resistor. During normal AC operation, the input supply provides power to both the OUT (system) and BAT pins. For peak or excessive loads (typically when operating from the USB power, PSEL = low) that would cause the input source to enter current limit (or Q3 – USB FET limiting current) and its source and system voltage (OUT pin) to drop, the dynamic power-path management (DPPM) feature reduces the charging current attempting to prevent any further drop in system voltage. This feature allows the selection of a lower current rated adapter based on the average load (ISYS-AVG + IBAT-PGM), rather than a high peak transient load.