Our homes are getting smarter by using internet-connected devices to enable the remote monitoring and management of appliances and systems. The video doorbell, an essential smart home accessory, provides high-definition images and two-way audio communication so that homeowners can greet visitors from their smartphone. While most video doorbells are hardwired to a 12V to 16V supply, many consumers are seeking solar- or battery-powered video doorbells when the existing wiring or transformer is out of date or incompatible. The battery is normally very small to support wireless connectivity and the doorbell button press. TI’s BQ25622 and BQ25638 buck chargers have an I_Q of 1.5µA in battery-only mode and 100nA in shutdown mode, with power path to maximize and extend battery run time throughout the product’s life cycle.

Enabling the essential functions of the device only when needed reduces I_Q in these chargers, which have a function to monitor the battery temperature through the TS pin for safety reasons. As shown in Figure 2, a switch internal to the chip isolates the external thermistor network connected to the TS_BIAS pin from the 5V REGN pin. This architecture helps eliminate 99% of the thermistor bias current affecting charger I_Q by enabling the internal switch with a 1% duty cycle.

Turning off the system voltages while maintaining battery power in ship mode can reduce I_Q even further. As shown in Figure 3, the BQ25622 and BQ25638 have an integrated, bidirectionally blocking internal field-effect transistor (FET) (Q4) that isolates the battery from the system in its off state. Ship mode is useful not only when the product is about to be boxed at the factory, but also when the device is low on battery, or when the user wants to power off the product.