How to reduce power consumption in embedded medical electronic applications
Abstract: Low power consumption is one of the goals pursued when designing any electronic device. In the case of portable medical devices , achieving power consumption goals is a key factor in the successful development of products. By integrating high-performance semiconductors with multiple functions in a single device with greater integration, designers can dramatically reduce the size of medical devices while reducing medical applications (including implantable devices, portable devices, home devices, and security devices). The power consumption in them to extend their life. This article will show how designers can take advantage of the advanced power management features of microcontrollers (MCUs) to reduce power consumption in medical applications.
Design issues involved in reducing power consumption System designers face many of the challenges presented by compact and portable medical electronics. Designing power supplies for low-power devices can be tricky because designers need to consider the system's voltage/current requirements. In many low-power applications, batteries are the primary source of power, presenting many challenges to designers in terms of chemistry, performance, capacity, size/weight, and cost. For example, high capacity batteries have higher internal resistance, which makes them unsuitable for high current applications. Compared to high internal resistance batteries of similar size, batteries suitable for high current applications are generally low in capacity and heavy in weight. In addition, the capacity of the primary battery that can only be discharged is much higher than that of the rechargeable battery. Because of these limitations, designers need to develop strategies for specific systems to achieve the best results in terms of cost and performance.
Static power consumption is an important quality indicator that indicates the suitability of an MCU for low-power applications. For some MCUs with advanced processing techniques, the current consumed in sleep mode can be less than 50nA. In order to be able to adapt to a variety of low-power designs, it is important to note that the MCU can operate over a wide voltage range. For example, when using an alkaline battery, it needs to be able to operate at 1.SV because the terminal voltage of each battery is 0.9V, and two batteries are usually used in applications. Selecting an MCU that operates over a wide voltage range extends the life of your portable device. However, the operating voltage range of the MCU is not the only determinant. The operating voltage range of the entire system must be considered, including the peripherals of the MCU. If a single peripheral in the system consumes most of the power, reducing the power consumption of the MCU has little effect on the total system power consumption.
As a design rule, if the system uses the MCU's internal peripherals (such as analog to digital converter or EEPROM), you must pay attention to its working range. If some peripherals are not able to operate over the entire operating voltage range of the MCU, the operating voltage range of the system will be determined by the peripherals. The same design rules apply to all peripherals as well. In the following sections, we will describe how some of the MCU family products currently available on the market offer special features for power management.
Method of reducing power consumption
Control peripheral power consumption
The core principle of portable embedded system power management is to enable the MCU to control the power consumption of internal and external devices. When designing a portable medical device, first determine the required physical mode or state, then split the design to turn off the unwanted circuitry. For example, a Brown-out Reset (BOR) function is not required in battery applications, so power can be saved by disabling this feature. Aiming at this goal, choosing the right MCU from many different vendors can help reduce external components and reduce costs. As mentioned earlier, MCUs that operate over a wide voltage range can diversify system designs.
Take an MCU-based medical data logger as an example. It contains sensors, EEPROM and battery, as shown in Figure 1. The medical device is a typical example of a low-power embedded design that takes sensor readings, scales sensor data, stores data in EEPROM, and waits for the next sensor reading. In traditional systems, EEPROMs, sensors, and their bias circuits may be powered at all times, but the power supply is not efficient. So how do you save power in similar systems? The answer is to turn them off by program control when they are not needed. In the example given, the designer can use the MCU's 1/0 pin and a few bytes of code to power the EEPROM and sensor as needed. Because the 1/0 pin can supply up to 20mA, there is no need to provide additional components to switch the power supply.
Figure 1 Application example of medical data recorder based on MCU
Power management mode
In embedded applications, a common way to save power is to periodically put the MCU into sleep mode when the system's resource requirements for the MCU are low. Then, to perform useful work, wake up the system's MCU by interrupt or after the watchdog timer expires. The longer the MCU is in sleep mode, the lower the average power consumption of the application. Just make sure that the watchdog's delay period is appropriate for the application. Generally, the working mode is as follows: If the application requires the MCU to process the sampling data at regular intervals, the watchdog timer should wake up the MCU once in the required time period. When using this function, you need to select the MCU that supports the corresponding watchdog cycle.
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