Ultra-low power MCU-How to reduce the power consumption of MCU

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Ultra-low power MCU-How to reduce the power consumption of MCU [Copy link]

Low power consumption is a very important indicator of MCU. For example, some wearable devices have limited power. If the power consumed by the entire circuit is particularly large, the power will often be insufficient, affecting the user experience. When we are making products, the basic functions are very simple to implement, but as long as it involves low power consumption, it is more difficult. For example, some MCUs can be as low as microamperes, but the low power consumption of the designed ones is always milliamperes. The current can be hundreds to thousands of times higher than the standard. Don't be afraid when you encounter this situation. As long as you are serious, you will win. Let's analyze the reasons carefully below. The first one: Cut off the lifeline of peripherals-turn off the peripheral clock Let's talk about the most intuitive aspect first, which is also the aspect that engineers pay more attention to, that is, turning off the peripheral clock of the MCU. For most MCUs on the market now, their peripheral modules correspond to a clock switch. Just turn on the clock of this peripheral and you can use it normally. Of course, this peripheral will also generate corresponding power consumption. On the contrary, if you want this peripheral not to generate power consumption, just turn off its clock. Second: Slow down the pace of work - don't multiply the clock In addition to the power consumption of the peripheral modules, there is another power-hungry user that needs attention, which is the PLL and FLL modules. PLL and FLL are mainly used to multiply the original clock signal, thereby increasing the overall clock of the system, and accordingly, its power consumption will also be raised. Therefore, before entering low power consumption, you need to switch to this mode, bypass the PLL and FLL modules, so as to reduce the power consumption of the MCU as much as possible, and then switch the clock back after the MCU wakes up. Third: Block the trickle - pay attention to the level status of the I/O port If you think that you can ensure that the peripherals no longer consume power by turning off the peripheral clock, then you are too naive. If the IO port is not handled properly, it will steal power in secret, and you are completely unaware. The specific reason is that there will be pull-up and pull-down resistors inside or outside the general IO. For example, as shown in the figure below, if an IO port has a 10KΩ pull-up resistor, pull the pin to 3.3V, but when the MCU enters low power mode, this IO port is set to output low level. According to Ohm's law, this pin will consume 3.3V/10K=0.33mA of current. If there are four or five such IO ports, then several mA will be attached, which is a pity. Therefore, before entering low power consumption, please check the status of the IO ports one by one: If this IO port has a pull-up, please set it to high-level output or high-impedance input; If this IO port has a pull-down, please set it to low-level output or high-impedance input; In a word, don't waste the best current on the function of generating heat, we don't rely on this temperature to warm our hands. Article 4: Good neighborly cooperation-pay attention to the coordination of I/O and peripheral IC The current consumption of the pull-up and pull-down resistors of the IO port is relatively obvious. Let's talk about a less obvious factor: the current consumption when the IO port is connected to an external IC. If an IO port has a pull-up, and the IC pin connected to the IO happens to have a pull-down, then no matter what level the pin is at, it will inevitably generate a certain amount of current consumption. Therefore, whenever you encounter this kind of situation, you first need to read the manual of the peripheral IC, determine the status of this pin, and know it well; then, before controlling the MCU to sleep, set the pull-up and pull-down modes and input and output status of the MCU's IO port to ensure that no current is consumed by it. Article 5: Disconnect the debugger and don't be fooled by illusions There is another peculiar type, where the detected current consumption is very large, but the actual result is that you are worrying too much. What is the reason? It is because the MCU is still connected to the debugger when testing the power consumption! At this time, most of the current will be taken away by the debugger, making the engineer extremely depressed for no reason. Therefore, when measuring low power consumption, be sure not to connect the debugger, and don't measure the current while debugging.