Block Diagram

The block diagram in Figure presents a high-complexity, compact size application example that showcases the functionalities necessary for numerous battery-operated devices powered by a standard 5V USB. Compared to the previously mentioned devices, the MCP73871 can charge the battery and supply voltage to the PMIC without requiring an additional System Power Path Management block. Therefore, the previously discussed workarounds are unnecessary as the MCP73871 includes an integrated system load sharing feature. This allows it to simultaneously power the system and charge the battery without concerns regarding charge termination. Subsequently, the PMIC generates the necessary voltage rails and provide an interface to the MPU.

Figure . Compact Size – High-Complexity Block Diagram Solution

The Battery Charge Management Controller features seven pins for interfacing with the MPU. Three pins are designated for signaling the status of the device and battery, while the remaining four pins are utilized for device configuration.

The configuration pins are:

  • CE - Device Charge Enable; Enabled when CE = High
  • SEL - Input Type Selection (Low for USB port, High for AC-DC adapter)
  • PROG2 - USB Port Input Current Limit Selection when SEL = Low (Low = 100 mA, High = 500 mA)
  • TE - Timer Enable; Enables Safety Timer when Active-Low

The status pins are:

  • PG - The Power Good Pin is an Open-Drain Logic Output for Input Power Supply Indication
  • STAT2 - Charge Status Output 2 is an Open-Drain Logic Output for Connection to an LED for Charge Status Indication
  • STAT1/LBO - Charge Status Output 1 (Open-Drain). Low Battery Output Indicator when VBAT > VIN

Therefore, the Battery Charge Management Controller handles several critical functions typically managed by the MPU or microcontroller. From the moment a battery or a power supply is connected to the MCP73871, it can perform a small diagnosis, so it can show the user:

  • if the voltage at the VBAT pin is less than the preconditioning threshold ➔ the device will enter a preconditioning mode
  • if the connectors of the battery are damaged, signaling that no battery is present
  • if there is a timer fault, which means that the system load substantially limits the available supply current to charge the battery
  • if the battery charge is complete
  • if the temperature is outside normal operating conditions ➔ the device will immediately suspend the charge cycle
  • if the battery voltage is low, meaning that it needs to be recharged, so that the MPU or microcontroller can inform the user that an AC-DC wall adapter or a USB port power source needs to be connected

All these functions alleviate the microprocessor from the need to independently implement complex circuitry in battery-powered applications to achieve the same functionalities.