Low-power MCUs, sensors, wireless communications, and efficient power supplies are critical to battery life.

As smart and connected products continue to shrink in size, expectations for their functionality and performance are rising. Batteries are also trending toward smaller sizes but longer lifespans. Low standby current is crucial for effectively extending battery life.

Medical patches for measuring body temperature, administering insulin, and monitoring heart rate have recently been released. The most crucial requirement for these devices is long-term, stable operation. However, these devices are often left in supply closets and medicine cabinets for long periods before being used. Furthermore, smartwatches, earphones, and video game controllers must operate for extended periods after a quick charge.

For countless sensors used in the field, such as electricity meters, gas detectors, and building automation systems, charging and maintenance are challenging, making guaranteed operating time essential. Most IoT devices rely on batteries to ensure long-term, stable operation in a variety of environments. Battery life has reached a major turning point.


Factors affecting battery life​

What are the key factors affecting battery life? System designers measure battery life based on the active, sleep, and hibernate currents of a central control unit, such as a microcontroller (MCU). Related sensors and wireless communication also operate alongside the MCU. Of course, the power supply, which supplies energy to all functional blocks in the system, is also crucial. Power supplies consist of regulators, such as step-down and step-up converters or low-dropout (LDO) converters. Some power supplies incorporate multiple power architectures or even power management integrated circuits (PMICs) that include a battery charger.

Operating current consumption is a critical factor in extending battery life, and battery runtime is ultimately affected by the time spent in each power mode. The standby current of each component becomes a critical factor when sleep and hibernation functions are in operation for extended periods. In this case, the standby current of the power supply is the largest contributor to the system's standby power consumption. Consider a system powered by a 40 mAh, 1.55 V silver oxide coin cell battery with a one-year lifespan. Assuming a current consumption of approximately 4 µA, reducing the current to 1 µA can extend the life of a wearable product by approximately three months.

Standby current is important for extending battery life.

Standby current should never be underestimated. When a power supply is in standby mode, power consumption is determined by quiescent current (I _Q ). This refers to the circuit's static state, when the circuit is not generating any load and the input is not circulating. While quiescent current is still nominally current, it significantly impacts the system's efficiency when operating under light loads.

Quiescent current is sometimes confused with shutdown current. In quiescent current, the system is idle but ready to wake up and operate at any time. This is the desired behavior of the device. Conversely, in shutdown current, the device is asleep. Designers use quiescent current to evaluate the power loss of the power supply under light load conditions. Shutdown current, on the other hand, is used to measure battery life when the device is powered off but the battery is connected to the regulator.

Devices are designed with components such as low-power MCUs, sensors, wireless communication, and efficient power supplies to extend battery life. Some designers opt for boost converters to extend battery life when the battery voltage drops to low levels. However, this method increases standby current and accelerates battery discharge unless the appropriate converter is selected.

The final product's form factor is also a key consideration. Consumers and designers prefer smaller, lighter products. The problem is that the battery is typically the largest and heaviest component on the entire board. While battery size can be reduced, this reduces capacity, which in turn shortens battery life. This challenge boils down to efficient power management techniques that balance capacity and size.

One way to extend battery life is to improve the system's power efficiency. Within a system, MCUs, sensors, analog front-ends (AFEs), and other load circuits must operate at voltages different from the battery voltage. Therefore, each circuit requires a dedicated DC-DC converter, which incurs efficiency losses. These circuits also require additional components, such as supervisory ICs supporting the MCU. "Protection" devices, such as current-sense amplifiers, temperature sensors, and comparators, help manage load and battery current for overall system management. Given the growing popularity of products that are not always on and remain passive, the standby current of the power supply, along with supporting components and protection devices, are key factors in extending battery life.

It's important to pay attention to the quiescent current specifications of power regulators, such as boost converters. Lower quiescent current can extend battery life. Considering today's ultra-compact designs, technology that not only reduces quiescent current but also achieves smaller form factors than existing products is crucial. Even milliamp-level currents aren't low enough to significantly impact battery life. Today's wearable, mobile, and IoT designs require nanoamp-level currents.