The BQ25172 is an integrated 800-mA linear charger for 1-cell to 6-cell NiMH battery applications. The device has a single power output that charges the battery. When the system load is placed in parallel with the battery, the input current is shared between the system and the battery.

The device charges a NiMH battery in constant current mode only and terminates the charge cycle when the programmable timer, t_SAFETY, expires or the battery voltage exceeds the V_{OUT_OVP} threshold. An optional intermittent charging phase can be programmed to automatically recharge the NiMH battery for a reduced timer duration once its voltage falls below V_RECHG.

The charger includes flexibility in programming of the charge current, charge safety timer duration, and series cell-count. This charger is designed to work with a standard USB connection or dedicated charging adapter (DC output).

The charger also comes with a full set of safety features: battery temperature monitoring, overvoltage protection, charge safety timer, and configuration pin (VSET, ISET, TMR) short and open protection. Upon application of a valid input power source, the configuration pins are checked for short and open circuits. All of these features and more are described in detail in the following sections.

The charger is designed for a single path from the input to the output to charge the battery. Once the input adapter has been connected, the charge current is applied and the safety timer is started. The charge current is programmed using the ISET pin. The safety timer is programmed by the TMR pin.

Power dissipation in the IC is greatest at high charge currents and low battery voltages. If the IC temperature reaches T_REG, the IC enters thermal regulation, slows the timer clock by half, and reduces the charge current as needed to keep the temperature from rising any further.

Further details are described in Section 7.3.