How to extend lithium battery life through a dual processor application

著者：Iflowpower – Dodavatel přenosných elektráren

In the face of the need to extend battery life, many system designers believe that the power consumption consumed by a single chip is less than the two chips. The reason seems to be simple: chip communication consumes more power consumption than a single chip, there are more transistors on both chips, so there are more leakage currents with single-chip with the same function. But power consumption technology has given this kind of traditional point of view.

DSP designers integrate more features, such as accelerators, communication modules, and network peripherals to the DSP chip, making the chip more useful to engineers. But this more powerful chip will consume more power consumption than this task in completing simple in-house management or monitoring tasks. In many cases, the designer cannot only enable the features required in the DSP chip.

In some applications, the microcontroller (MCU) performs the same system monitoring task, which is more power consumption than DSP. So, the architecture of the double chip: DSP and MCU are also possible. Therefore, use a low power DSP as a main processor, another low power MCU as a system monitor, can extend the battery life consumed by the single DSP to complete the same task.

To help save power, engineers should consider the following factors when choosing DSP: look for larger capacity on-chip memory. DSP always consumes more power consumption when accessing the chip exterior memory. External DRAM stores constant power consumption, which consumes battery electrical energy.

Choose a DSP that can start and close peripherals. Some DSPs can automatically power off on the inactive on-chip peripherals, which supplies a variety of control and power consumption provinces. Select a DSP that enables a variety of standby states at different power levels.

Multi-power supply saves more energy consumption. Choose DSP for the development software that optimizes power consumption and reduces power consumption. Tools should make developers easily change the voltage and frequency of the chip, manage power status, help them evaluate and analyze power information.

MCU consumes less current in some applications in the MCU in some applications, low-power semiconductor process reduces transistor leakage current to help chip designers optimize low power operation. Unfortunately, low power consumption will limit MCU performance. For example, a TEXASINSTRUMENTSMSP430MCU consumes 500NA current in standby mode, the maximum clock frequency is 16MHz.

The maximum clock frequency running in TMS320C5506DSP is 108MHz, consumes 10 in standby modeµA current. This indicates that it consumes 20 times higher than the MSP430.

From the previous development process, the internal MCU peripheral has been controlled by the software, which indicates that the CPU maintains active status. But the new interrupt drive (Interrupt-Driven) is peripheral for less software overhead, allowing MCU to keep standby mode in most time. Take the internal modulus converter (ADC) hardware as an example, it automatically scans the input channel, trigger conversion, and execute DMA transmission to process the received data sampling task.

As a result, the ADC is almost spontaneously running. The CPU only uses very little time for its supply service, and the MCU saves power consumption. Multiple clock reduction power requirements MCU clock system design can also help reduce power consumption.

The circuit diagram in Figure 1 shows two clocks operating by a single crystal. The MCU usually uses a 32kHz crystal, but does not necessarily generate internal clock signals, system clock (MCLK), and secondary clock (ACLK) signals. Typically, crystals only generate ACLK signals.

MCU's low-power extraction using a 32kHz auxiliary clock that simultaneously drives the MCU real-time clock, high-speed digital control oscillator (DCO) generates a system clock signal for CPU and high-speed peripherals. DCO can generate clock signals in several ways, each with different performance and power consumption characteristics. From low to high power consumption, these clock modes have ultra low power oscillators (VLO), 3kHz crystals to DCO.

In order to reduce power consumption, the designer uses the lowest clock (VLO or 32kHz crystal) in idle mode, and realizes high frequency DCO when the activity is applied to the CPU. DCO can be less than 1µThe time of S's time enters the active state and is fully stable. This instant enabled capability saves time and power consumption.

Note that the low-power clock using low frequencies is consumed to consume more power than the faster clock during activity processing. In higher power-consuming mode, low frequency time bells the CPU spend more time on a specific task. In addition to using low-speed clock-saving power consumption on certain peripherals, the MSP430MCU also supplies ultra-low power oscillators to generate an ACLK signal.

Under its standby power mode (LPM3), MSP430MCU usually consumes less than 1 in ACLK operation and all interrupt enabled statesµA current. Therefore, low-power MCUs consume less power than DSP during the real-time clock or management battery charging.

Moreover, the Task is given to the MCU or the DSP can be freed, so that it can perform the signal processing task of its good at. Power consumption saving results engineers can see the dual processor design to achieve excellent results. Imagine a system that relies on high-end DSP to handle monitoring tasks.

The processor will quickly use the other 2,500mAh nickel-hydrogen AA battery. If the average current consumption is 10mA, the two series batteries will be exhausted within 10.5 days.

Dual processor applications reduce current to 1mA to extend the battery to 120 days. The MCU in the dual processor system is reduced power consumption, some system or monitoring functions that can be processed include: real-time clock maintenance power sorting power monitoring and reset keyboard or human-machine interface management battery management display control management DSP power Many DSP must Apply a plurality of power rails of the power supply in a fixed order to ensure normal work of DSP and peripherals. Typically, these tracks simultaneously powered by core (CPU) and DDR memory and I / O devices.

Although dedicated devices can apply a voltage to the DSP chip by fixed order, it cannot perform other functions. Smaller low-power MCUs can be sorted and monitored for power supply voltage, and perform power control tasks (Figure 2). In this case, the software starts three power supply regulator circuits in an appropriate order.

The MCU uses its internal ADC to detect the appropriate voltage when the respective power rails are used. When the total circuit does not want a DSP chip, the MCU can turn off the regulator to close the DSP. In fact, the MCU can communicate directly with the pressure-controlled oscillator to control the voltage and frequency of the DSP, or the clock frequency of the PLL communication control DSP.

Therefore, when the DSP completes the computational dense task, the MCU adjustable clock converts the DSP to standby mode to save power consumption. Bidirectional monitoring allows MCU to detect DSP to understand its busy state. In this mode, the MCU is running as a smart controller.

On the other hand, DSP can read and write the MCU. So the DSP can notify the MCU to reduce or improve the DSP clock according to the application. Using the MCU to complete DSP usually achieved other tasks implemented in a single processor system, designers can also get more benefits.

For example, when processing the keyboard operation, the MCU consumes less power consumption than the DSP. The MCU sends an interrupt signal to the DSP only after detecting the operation of the button or the release of the button. This approach helps prevent excessive current consumption caused by hit, which often appears in some handheld devices.

In order to further relieve the load of the DSP chip, the MCU can supply: the drive circuit standard SPI, UART and I2C ports for radio frequency communication peripherals are used for the above and previously mentioned. Each peripheral, the MCU can automatically start from low power mode. Therefore, the MCU will not continue to poll the peripherals to determine which service, does not consume the maximum power consumption to make this task.

Peripherals will be started. Each milliwat in low power consumption is very valuable. Finally, the designer must determine the use of one or two processors in the application based on computational, measurement, and functional considerations between DSP or MCU.