Tips for Extending Battery Life for Portable Industrial Measurement Applications

Battery life is critical for portable applications. For applications such as smoke detectors, security devices, and thermostats, the factory-installed battery needs to last for more than 10 years. Therefore, extending battery life has become a key component in the design of portable applications.

To maximize battery life, designers need to minimize the average current consumption of the system. To achieve this goal, it is very important to use multiple low-power operating modes and choose the right components. As for low-power operating modes, these include shutdown mode and real-time clock standby operation mode. The main components include: microcontroller (MCU), power supply and signal chain elements. As various MCUs vary more and more in terms of cost, peripheral design, CPU architecture and on-chip resource integration, it becomes more challenging to choose the best MCU for a specific application.

For portable industrial measurement applications, to select the most suitable MCU, it is necessary to prioritize the key application requirements, such as longer battery life, high-performance analog peripherals and rich user interfaces. The right article talks about some tips for achieving the longest battery life for designers' reference.

should

1.Try to minimize the current consumption in standby mode. In many portable applications, the CPU is idle for more than 99% of the time. In this case, the current consumption gradually transitions to idle mode, in which you can enter a full shutdown mode or a mode that waits for an external interrupt until it is woken up, and you can use the timer for real-time clock operation.

2. Choose an MCU with the shortest wake-up time. The MCU consumes the most current in operating mode. During the MCU wake-up process, that is, when it enters the operating state from idle mode, the CPU consumes a much higher value of operating mode current. Therefore, designers should consider choosing an MCU with the fastest wake-up and code execution speed. Generally speaking, we define the time from the interrupt generation to the clock recovery fast and stable operation as the wake-up time. In the figure, the interrupt wake-up time of the Texas Instruments MSP430F20x1 is less than 200 nanoseconds.

3. Use low-power brown-out reset (BOR) protection. Any portable application requires a BOR or low-voltage detection function to ensure that the system automatically resets when the power supply voltage drops below the specified value. Many MCUs have brown-out protection, but they also add an additional 20 to 70 microamps of current consumption. Since this protection function must always be in operation, designers should consider using a low-power BOR function. For example, TI's MSP430 16-bit MCU has a "zero" power brown-out reset protection function.

4. Increase integration as much as possible. Some MCUs integrate functions that eliminate the need for high-resolution A/Ds, operational amplifiers, and 12-bit D/A on the board. These integrated functions allow register communication, replacing serial communication that consumes more current. Adding any components to the circuit board will increase leakage current.

Should not

1. Select an MCU based solely on the front page of a specification. Designers must carefully read the complete data sheet and pay attention to the worst-case operating temperature, extreme parameters, and operating voltage.

2. Assuming that the operating modes of MCUs from different vendors are similar. In fact, the current consumption values ​​of MCUs vary from vendor to vendor. For example, a certain MCU vendor may not provide all the functions that are common under a given operating condition.

3. Use multiple power supplies. Some designs require multiple or complex power supplies. Since the power supply must continue to work in most cases, using a low-dropout regulator or boost converter may be expensive because it not only increases the cost but also results in a higher average current consumption. Consider using a 3V power supply.

4. Use polling monitoring. Some MCUs recommend using an infinite loop so that you can loop and monitor all the peripherals you want to monitor. This is an inefficient method that increases the CPU load and increases current consumption. Consider using an MCU with excellent interrupt function support. For example, some low-power MCUs have interrupt vectors that support up to two 8-bit ports, while other MCUs only support a very small number of I/Os.

5. Improper use of the CPU. A general recommendation is to read the user manual carefully to ensure that you are taking full advantage of the features provided by the MCU. It is important to realize that for every line of useless code that is executed, some battery power is wasted. A low-power MCU should have hardware features that keep the CPU powered off while the peripherals are performing specific tasks that do not require any processing. For example, with auto-scanning, an A/D converter can automatically scan different channels and store the values ​​in a temporary buffer, flash memory, or RAM without involving the CPU.