With the rise of portable mobile devices and various wearable technologies, we must pay attention to the power consumption issues of these devices, as they all share a common characteristic: they are powered by battery systems. A single circuit board may contain many unit circuits related to power consumption. Today, we will discuss the low power issues concerning MCUs.
When addressing this issue, the first step is to select a low-power MCU. Generally, the power consumption of an MCU is specified in the electrical properties section of its corresponding reference manual. Secondly, when using an MCU in low power mode, we often encounter significant discrepancies between actual and theoretical power consumption. In such cases, it is essential to carefully check the following points.
1. Disable Peripheral Clocks
The clock is akin to the heart of a person; the normal operation of peripheral modules cannot be separated from the clock. For most MCUs, peripheral modules have a clock control switch. As long as the peripheral clock is enabled, the peripheral can function normally, but it will also generate corresponding power consumption. If this peripheral is not needed, be sure to turn off its clock to reduce power consumption.
2. Adjust Clock Frequency
Typically, when using a microcontroller, we tend to set the clock frequency to the highest level right away. The advantage of this is that the execution speed of the program increases, as the period T = 1/F. Generally, we use the internal PLL frequency multiplication module of the microcontroller to multiply a low input frequency to a high frequency. On one hand, the frequency multiplication module increases power consumption; on the other hand, the corresponding peripheral module’s operating frequency increases, leading to higher power consumption as well. You will notice that in low power mode, the operating frequency of the microcontroller is very low, so when considering power consumption, do not forget to consider the clock frequency.
3. Pay Attention to IO Pin Voltage Levels
Be mindful of the states of unused IO pins and the internal pull-up or pull-down configurations, as these can accumulate and lead to increased power wastage. Moreover, fundamentally, we should not only focus on the idle states of IO pins; for the IO pins in use, we also need to consider their states during normal operation, in conjunction with the peripheral circuits for better results. For example, if we need to light an LED, and the microcontroller’s IO pin continuously outputs a high level to keep the LED lit, could we consider an alternative approach where the LED lights up when the microcontroller outputs a low level? This way, we can save some power through cumulative effects.
4. Disconnect Debuggers and Testing Tools
During testing, we typically connect various testing tools to assist with debugging. These auxiliary debugging tools may be powered by the circuit board, and you might mistakenly attribute this power consumption to the MCU. Of course, it is not only important to focus on the power consumption brought by testing tools, but also to consider your testing methods. It is very likely that your testing method is incorrect or that the testing tools themselves also consume power.
Designing low power consumption for MCUs is a meticulous task that requires developing good habits. For each additional peripheral function module, we can test the corresponding power consumption brought by that peripheral. This includes measuring the increase in power consumption due to added functionality, as well as the static power consumption of the module and its power consumption during normal operation after integration into the system. We must always keep track of the module’s dynamics. We should consider not only the internal clock states and clock frequencies but also the coordination between IO and peripheral circuits, etc., to reduce some power consumption by adjusting the circuit’s operating methods. Of course, there are more factors affecting MCU power consumption than just the points mentioned in this article. Do you know of any other reasons that influence the power consumption of MCUs? Feel free to leave a comment to share with everyone!
Previous Reviews:
● Plain Language Explanation of ModBus Protocol
● Discussing Memory Pointer Operations
● Matters Concerning Heap Memory
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