Standby, sleep, power saving, hibernation, and shutdown functions are crucial for designers to reduce power consumption and extend battery life. In each mode, the current during sleep can easily vary from a few mA to nA.
The advent of wearable devices has made this task more difficult, partly due to the need for smaller batteries to ensure small factors. The trend towards smaller batteries to accommodate smaller, lighter, and more powerful electronic devices has led to some compromises. The Internet of Things (IoT) and all connected devices have increased this need, requiring reliable operating modes for extended periods and under a variety of operating conditions. Battery-powered systems require careful partitioning, compact space utilization, and efficient use of available power.
The high efficiency of these devices is first demonstrated during the necessary long standby periods. In these cases, energy consumption is defined by quiescent current (IQ), which is different from shutdown current. It is the operating state of the circuit when no load is controlled. Quiescent current is often confused with quench current, which is the current absorbed when the device is off, but the battery is still connected to the system.
Why ultra-low quiescent current?
While active current consumption is a significant factor in extending battery life, the battery's actual lifespan also depends on other operating modes, particularly standby mode. The current drawn during standby (Iq) must allow the device to be woken up at any time to execute requests from the microcontroller.
Iq is a primary indicator of standby power consumption in electronic systems and an important design parameter for modern low-power DC/DC converters used in power management circuits. Iq can assess various factors, such as power consumption under small loads.
Power management typically consists of voltage regulators, such as switching regulators that increase or decrease voltage, or regulators with low dropout (LDO) voltage. Some involve more complex architectures, potentially even the charger itself. Lowering Iq improves efficiency, thus extending battery life by consuming less battery power.
Power supply design
Power management circuitry includes multiple DC/DC solutions for powering sub-components in devices such as sensors and microcontrollers (MCUs). The low power of the MCU impacts the overall system's energy efficiency. MCUs come in various form factors, sizes, and architectures, but for connected IoT devices, a 32-bit ARM microcontroller is a good choice. These MCUs are well-supported by multiple manufacturers and are relatively easy to develop robust and portable software for.
The manufacturing processes used to produce electronic components also affect energy efficiency. For example, advanced CMOS processes help ensure proper battery usage while reducing consumption. Designers need to balance capacity and size through efficient power management techniques. Improving system energy efficiency is a common method for extending battery life.
The power management section involves using voltage monitors to ensure the proper functioning of the entire power system. If a voltage interruption occurs, the monitoring solution must issue an error signal so that the rest of the system can shut down correctly. A fast start-up delay allows voltage faults to be detected before the rest of the system starts up, providing maximum safety under hazardous conditions. Texas Instruments (TI)'s TPS3840 Nanopower high input voltage monitor, featuring manual reset and a programmable reset time delay, provides this high-precision solution.
As the portfolio of mobile devices grows year after year, lithium-ion batteries require extra care through dedicated charging cycles to maximize battery life. Charging batteries for wearable devices is challenging because the batteries must be small in size and large in capacity.
TI also offers the BQ25619, a new switching integrated battery charger (IC) that supports a 20 mA cut-off current. It increases battery capacity by 7% and reduces battery leakage to 6% in transport mode. This device enables designs for more efficient medical and personal electronics applications, such as hearing aids.
DC/DC solutions
Choosing the right power management device for your application is related to the architecture of your DC/DC solution. Factors to consider when selecting a DC/DC solution include quiescent current (lower values are always better) and efficiency (higher percentages mean longer battery life). Ideally, you should have >90% efficiency at the µA level. Another parameter is the range of input voltages that allow operation even when the battery is almost depleted.
Power management integrated circuits (PMICs) include a dozen or so line-dependent voltage regulators (LDOs). LDOs are also integrated into microprocessors, graphics processing units (GPUs), and many other system-on-a-chip (SoCs). The two main categories of voltage regulators are linear regulators (LDOs) and switching regulators.
Switching power supplies will undoubtedly be widely used due to their advantages in power density and overall efficiency. However, LDOs are used because they offer lower output voltage noise, smaller size, and lower cost compared to switching regulators. A trade-off is typically made between achieving very low Iq and simultaneously meeting other key parameters such as excellent dynamic performance, low output noise, and high power noise rejection.
TI has introduced the TPS7A02, an ultra-low-power, low-dropout (LDO) linear regulator that claims an industry-low Iq of less than 25 nA, one-tenth the size of competing ultra-small devices. The new controller allows engineers to at least double battery life and boasts best-in-class transient response for faster wake-up times, improved application response times, and dynamic performance.
In addition, the small size allows designers to reduce the size of the final product, making it the best choice for all wearable applications.
The TPS7A02 can reduce the size of solutions by 70%, enabling engineers to add more functionality to their designs in space-constrained applications or reduce system costs by using smaller circuit boards.
The TPS7A02 is designed for low-power applications such as power grid infrastructure, building automation, and medical devices (Figure 2). By using the device in wireless video doorbell and security camera designs, engineers can achieve battery life of 24 months or more (up to four times the industry standard).
“As consumers look to reduce the frequency of charging or replacing batteries, there is a growing demand for electronics that offer longer battery life, higher efficiency, and smaller size. Low quiescent current plays a crucial role in helping engineers address all these challenges,” said Mike Beckman, vice president at Texas Instruments (TI). “That’s why TI continues to focus on developing and delivering innovative low-Iq DC/DC converters, LDOs, battery management systems, and other power components to help engineers solve the design challenges surrounding small, low-power, long-life industrial and personal electronics.”
TI also offers the TPS62840, an ultra-low-power switching regulator with an operating IQ of 60 nA. Its wide input voltage (V<sub>IN</sub>) range of 1.8 V to 6.5 V supports a wide variety of battery chemistry and configurations. It can be used in many battery-powered, always-on industrial and personal electronics applications, including narrowband IoT, grid infrastructure equipment, and wearable devices.
Both of these ICs operate with very low quiescent current, providing a simple solution to help improve battery life in any battery-powered device. The significant reduction in quiescent current can allow applications to run for seconds, minutes, hours, or even days.
