In Part II of our consumer application series, let’s take a closer look at the role power management plays in system designs. Power management is another function best performed by an “Always ON” ultra-low-power system controller like an MSP430 device. The reason for this is two-fold. First, battery charging and monitoring needs to happen consistently every few minutes or even seconds. An application processor takes longer to wake up and consumes more power than an ultra-low-power MSP430 microcontroller does to complete this same function. Secondly, from a system architecture standpoint, polling the battery charger, fuel gauge and temperature sensor using an application processor is a “distraction” from running the operating system (OS) and focusing on the user experience. Additionally, design teams for power are usually different from the team working on the application processor. Separating the power management controller allows for more autonomy in architecting the solution.
Key roles of MSP430 microcontrollers in power management applications follow with pertinent application notes hyperlinked or listed below:
- Initialize and monitor single- and multi-cell battery chargers (i.e.bq24230 and bq76PL536)
- Continuously monitor cell undervoltage, overvoltage and temperature monitoring
- Ensure safety of the battery and detect failure
- Detect battery insertion/removal
- Detect the charge/discharge modes
- Passive cell balancing for multi-cell batteries – so that all cells are optimally used
- Status indication (i.e. LED)
- Initialize user configuration and monitor fuel gauge (i.e. bq27425)
- Initialize fuel gauge based on battery chemistry and other characteristics
- Continuously monitor status such as temperature, voltage, remaining capacity and average current
- Execute state machine to determine when to charge/discharge the battery and whether the device runs from battery or power supply
- Periodic communication of battery/fuel gauge state to the host processor over I2C, USB, SMBus or PMBus
- Support firmware updates for battery/fuel gauge
- Authenticate chargers/batteries used in the system
- In some very low-cost applications like power bank, the MSP430 microcontroller can work as a power system controller. For example, in case of Li-Ion battery chargers, state machines for slow charge, constant current charge and constant voltage charge can be easily implemented on MSP430 microcontrollers using the on board ADC to measure voltage and current and PWM timer to control charging.
Relevant application notes:
- MSP430 Based Lithium-Ion Polymer Battery Charging and Gauging Solution Using USB (Rev. A)
- MSP430 Microcontroller Software for Handheld Fuel Gauge & Battery Authentication (Rev. A)
- Multi-Cell Li-Ion Battery Management System Using MSP430F5529 and bq76PL536
- Implementing SMBus Using MSP430 Hardware I2C (Rev. A)
- PMBus Implementation Using the MSP430 USCI (Rev. A)
MSP430 interfacing to a Multi-cell battery charger (bq76PL536)
MSP430 interfacing to fuel gauge (bq27425)
MSP430 as a controller in a battery charging application