S3C2440A embedded handheld terminal power management system

　　Power Management (PowerManagement, PM) is an essential technology in electronic systems. Due to the adoption of advanced power management technology, mobile phones, PDAs and other products have been widely used. If perfect power management technology is not adopted, the talk time of a mobile phone may not exceed 2 minutes. As people's requirements for the functional level of embedded handheld terminal devices continue to increase, the power consumption of handheld terminals is also increasing. Paradoxically, the size of handheld terminals continues to shrink and the working hours continue to extend, putting increasing pressure on the power system management of embedded handheld terminals. How to design a power management system with stable performance and low power consumption has become one of the difficulties in the development of embedded handheld terminal equipment. This article focuses on the handheld terminal power management system based on microprocessor S3C2440A.

　　1Power supply requirements

　　The CPU of the handheld terminal adopts Samsung's ARM920T core processor S3C2440A. S3C2440A is a high-performance embedded microprocessor specially designed for various handheld terminals. Its main frequency can reach 400MHz. It has the characteristics of rich peripheral interfaces, small size and low power consumption.

　　S3C2440A has 4 working modes: normal mode, slow mode, idle mode and sleep mode. The four modes can be converted to each other. The difference mainly lies in the processor operating frequency, operating voltage and device combination. This design mainly uses different power management strategies for normal mode and sleep mode.

　　1.1 Power supply requirements in normal mode

　　In normal mode, the CPU and peripheral components require power. Peripheral components mainly include Flash, SDRAM, GPRS, GPS, wireless modules, LCD, touch screen and other parts. The hardware structure is shown in Figure 1.

　　The CPU voltage is divided into 2 groups: the core voltage is 1.2V; the I/O pin voltage is 3.3V. USB and GPS power supply voltage is 5V. The power supply circuit of LCD is relatively complex and requires a dedicated driver chip to power it. Since almost all handheld terminals now have color screens, LEDs used to adjust the brightness of the LCD backlight also require special drive circuits. The rest (such as GPRS, wireless modules, audio, etc.) are all 3.3V.

　　1.2 Power supply requirements in sleep mode

　　The CPU spends more than 90% of its time in sleep mode. The quality of power management in the sleep state plays a decisive role in the length of working time of the handheld terminal. Figure 2 shows the power supply requirements of the handheld terminal in sleep mode.

　　In sleep mode, the external device needs to provide 1.2v/1.3V voltage for the CPU internal energy control module through the VDDalive port, and provide 3.3V voltage for the memory interface power supply VDDMOP, ADC port power supply VDD_ADC, and I/O port power supply VDDOP. The real-time clock needs to be powered during sleep mode and system shutdown. PWREN is a control signal. After the CPU enters sleep, PWREN is low level. Unused modules in sleep mode can be turned off through this pin.

　　2Power management strategies

　　2.1 Power management strategy in normal mode

　　Power management in normal mode mainly achieves the purpose of saving energy by controlling the switches of peripheral controllers. S3C2440A has rich peripheral interface controllers, but these controllers may not all be used at the same time. By setting registers, unnecessary functional modules can be selectively turned off, and unused controllers can be turned off as much as possible to save power consumption as much as possible. Because if you don't turn them off, they will still draw current even if they are not in working condition.

　　2.2 Power management strategy in sleep mode

　　In sleep mode, the Time-out strategy is mainly used, as shown in Figure 3. After the system completes all tasks, if the duration exceeds a certain threshold (the time interval can be set by the timing module provided by the system), the power management module will convert the system to a sleep state until a new task request arrives and then wake up the system, then execute Task. In this way, the power consumption of system equipment is reduced.

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