Charger circuit powered by USB and adapter

Many charger ICs today have power-down control (Figure 7). Integrating this functionality goes beyond simply replacing external components. Because the integrated charger understands the operation of the switching circuit, it helps improve switching when the power supply changes.

Figure 7. Dual-input chargers such as the MAX8844 handle chargers powered by USB and adapters. The device also features input overvoltage protection up to 28V.
A common design consideration with chargers is the issue of powering from multiple sources , especially with circular connectors that may be connected to the incorrect adapter. To avoid such an event, the MAX8844 disables charging from input supplies higher than 7.5V, and can withstand and block inputs up to 28V, effectively protecting the battery, charger, and downstream circuitry from being mistakenly connected to any other type of adapter. . In addition, the MAX8844 features an overvoltage-protected LDO biased from the USB and adapter (IN) inputs that can deliver 30mA to the system. These LDO outputs (SAFE USB and SAFEOUT) remain active whether the charger is enabled or not . Other charging functions performed by the device include battery detection, thermal limiting, reducing charge current at extreme ambient temperatures (to maintain lower die temperatures), auto-starting logic outputs, and notifying the system when external power is applied.