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
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 AC or USB). If the primary source is not available, then the IC automatically switches
over to the other 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 adaptor or USB port).
The bq24038 replaces USBPG with pin VBSEL, to enable user
selection of the charge voltage. In addition, pin ACPG was modified to
PG. PG is active low when either ac power or USB
power is detected.
The ISET1 pin programs the battery&3146;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 adaptor based on the average load
(ISYS-AVG + IBAT-PGM ) rather than a high peak