When you're evaluating portable consumer electronics, you're likely to weigh a range of factors before opening your wallet. Lifestyle fit, product features and battery life might be on your list. That's why the companies designing these products continue to face the same power management challenges—they need to safely extend runtime while optimizing battery performance.
In the face of massive investments in artificial intelligence (AI), augmented reality (AR) and virtual reality (VR) technologies and voracious consumer demand, the need for robust power management will continue to grow. Therefore, system design must revolve around efficient use of the power provided by smaller batteries to support more advanced functions.
From a design perspective, the system engineer must understand the basics, such as when the battery is fully charged and should be disconnected from the charger, and when the battery voltage is discharged and should be connected to the charger. Optimizing charging and managing battery temperature tolerance for better power management performance further complicates system design challenges.
Most systems use a microcontroller (MCU) to monitor and control battery power and to indicate low or full battery status. Dedicated battery management solutions also provide an excellent way to optimize battery performance.
In all cases, battery monitoring and management circuitry will control one or more of these key factors affecting battery life:
How much current the battery can supply for a specified output voltage range during a specific period of time
How much current the battery can draw (during charging)
The voltage level that can be charged (or the maximum safe voltage)
The voltage class (or minimum safe voltage) that can be used
Temperature range tolerance level
The maximum safe operating voltage indicates that the battery is fully charged and ready for use. The minimum cut-off or disconnect voltage indicates when the battery is depleted. Attempting to charge above the maximum safe operating voltage is possible, but carries the risk of shortened life and other potentially catastrophic consequences. The same risk applies when falling below the discharge voltage level.
All of the above factors affect the inherent thermal stability and longevity of the battery. Therefore, voltage and temperature monitoring is critical.
A comparator with a window function is a cost-effective solution for monitoring battery voltage. This solution requires no additional software and reduces power consumption by allowing the system MCU to monitor the battery voltage in sleep mode while simply responding to the comparator flags. Additionally, the comparator circuit is small, making it ideal for applications with board space constraints.
The example shown uses the hysteresis of the desired voltage comparator to monitor the battery voltage. V TRIP_HIGH is the charge voltage and V TRIP_LOW is the discharge voltage. When the output goes low, an interrupt is signaled to the controller, it can be either a low charge voltage or a high charge voltage – the controller has to figure out which one it is.
Maxim's MAX40000, MAX40001, and MAX40002-MAX40005 series of comparators provide low-power, small size, and internal references with less than 1 µA of quiescent current. These specifications make it suitable for power monitoring with stringent power consumption requirements. The low quiescent current of the comparator is comparable to the current typical self-discharge rate of the battery, making it suitable for applications involving long sleep times or low duty cycles and long battery life requirements.
Reviewing Editor: Guo Ting