The bq25040 is an integrated Li-ion linear battery charger targeted at space-limited portable applications. It operates from either a USB port or AC adapter and charges a single cell Li-Ion battery with up to 1.1A of charge current.

The bq25040 has a single power output that charges the battery. A system load can be placed in parallel with the battery. The charge current is programmed using the ISET and EN/SET inputs. The input current limit is programmable to USB100, USB500 or a user programmed current limit up to 1.1A. Additionally, a 4.9V ±3% 50mA LDO is integrated into the IC for supplying low power external circuitry. The single-input interface (EN/SET) is used to select the charge current and to place the bq25040 into Production Test Mode. In Production Test Mode, the bq25040 operates as a linear regulator without a battery connected, where the output is regulated at 4.2V and supplies up to 2.3A to calibrate GSM transceivers.

The battery is charged in three phases: conditioning, constant current and constant voltage. In all charge phases, an internal control loop monitors the IC junction temperature and reduces the charge current if an internal temperature threshold is exceeded.

The charger power stage and charge current sense functions are fully integrated. The charger function has accuracy current and voltage regulation loops, charge status display, and charge termination.