Silicon Labs Ultra-Low Power Single Battery Powered MCU Series Introduction

Today's electronic products have higher and higher requirements for low power consumption, which is a problem that engineers must face. In the design process of low-power products with MCU as the core, the hardware and software aspects are generally taken into consideration, so choosing a low-power MCU becomes the key.　 

The main problems that are common and faced by current MCU low-power products are: 

1. The operating voltage is generally 1.8V, and it is difficult to reach below 1.5V, because the voltage cannot be too low to take into account the IO output capability of the processor, but the actual situation is that the lower the operating voltage, the better.

2. In the product design process, Wangwang requires the chip to have a higher degree of integration, be able to run at high speed and have a low-power working mode. In this working mode, the working current per MHz must be low enough; the switching from low-power mode to working mode requires a short time and a small current. 

3. Wake-up must be fast, which conflicts with standby low power consumption. 

4. When equipped with a real-time clock RTC, the standby current is difficult to reduce.　 

In response to these problems, Silicon Labs has specially launched a low-power MCU series with industry-leading concepts, which has the following features: 

1. Built-in Boost boost circuit, which can work normally at an input voltage of 0.9V. 

2. Built-in LDO provides hardware guarantee for low power consumption and stable operation of MCU. 

3. Ultra-low standby power consumption, the standby current is as low as 10nA when RTC is not working; when RTC is working, the standby current is as low as 300nA. 

4. The lowest power consumption in the industry is 160uA/MIPS when working. 

5. The AD converter design optimized for low power consumption can work normally when the input is 0.9V, and has Burst burst sampling mode to reduce the burden on MCU. 

6. Rich wake-up modes greatly improve the flexibility of system design and enable MCU to be in standby mode frequently. 

Silicon Labs' unique low-power design--power management unit PMU 

This design can realize the digital circuit working at 1.8V. Through the internal DC-DC function, the voltage provided by the battery is relatively low, and it can also provide 3.3V IO drive output, which can drive LED, wireless communication devices, etc. See Figure 1 



Figure 1 DC-DC block diagram 

In the power management of MCU, the power supply for IO module and analog unit can select the voltage converted by DC-DC module, or directly select the external power supply VDD. The stable power supply of 1.8V converted by LDO can be used for the MCU part to work and power the internal RTC, PMU and RAM; for the internal RTC, PMU and RAM, the battery can also be flexibly selected to directly power them. 

Rich standby and wake-up modes 

The wake-up time of the digital and analog parts of the C8051F9xx series is 2μS in the sleep state; when the RTC is not working, the current is as low as 10nA in the low-power mode, and only 300nA when the RTC is working.

Unique AD sampling working mode 

The ADC has a sampling rate of 300Ksps in the case of 10-bit sampling, and the burst sampling working mode can reduce the operation instructions and working time of the MCU. In the burst sampling working mode, after the sampling starts, the ADC powers on and tracks the input signal. Through voltage conversion, it enters the low-power mode of power-off after one system clock, waiting for the next sampling to start. During the entire sampling process, the MCU program does not need to perform power-on and power-off operations, which effectively reduces power consumption. The following figure is: 　 



Figure 2 Burst workflow 

low power implementation Take 

a low power design as an example, its basic mode is: wake up once every 0.5 seconds, perform ADC sampling, complete digital processing, and then sleep in a cyclic working mode. When the system works for a long time, the battery voltage will gradually decrease, so that the battery cannot supply power normally; the battery voltage of the Silicon Labs system drops slowly, and the battery life can reach about 1100 days, while other brands of low-power MCU applications cannot. See Figure 3 [page]




Figure 3 Comparison of Silicon Labs system with other similar products 

When the MCU is in sleep mode, it has very low current and its wake-up time is only 2μS; when the system is working, the MCU runs very fast, including the ADC sampling rate is also very high. Since the MCU consumes more power when working, it needs to complete the function quickly and enter the sleep mode. 



Figure 4 

As shown in Figure 4 above, if the Silicon Labs system clock is 25MHz, the working current can be slightly larger, and the working time is very short, and the power consumption is calculated by the product of the working current and the working time, that is, its "area". Although the working current of other application systems is relatively small, the working time is much longer, and the total power consumption "area" will be much higher. 

Silicon Labs' current product series 

Silicon Labs has launched the C8051F90x/91x/92x/93x series. 



Figure 5 Silicon Labs C8051F90x/91x/92x/93x series functional block diagram 

These series include rich peripheral resources, as follows:  

1. 24.5MHz built-in oscillation circuit. 

2. 2 independent comparators. 

3. UART, SPI, I2C communication interface. 

4. RTC real-time clock. 

5. PCA module can realize PWM, frequency, edge capture, timer and other functions. 

Product application (see Figure 6 below) 



Figure 6 

Development tools 

Silicon Labs' authorized agent Shiqiang Telecom can provide a complete development kit, C8051F912DK; it contains development software, data sheet, programmer, development board and power supply. 
In addition, you can also obtain application notes for related products from Shiqiang Telecom, including: 

AN358: C8051F9xx Optimizing Low-Power Operating Modes 

AN359: C8051F9xx Debugging Tips 

AN431: C8051F93x-C8051F90x Software Design Guide 

The single-battery powered low-power MCU, with its high integration, low current, low power consumption in operating mode, fast wake-up, and fast data processing capabilities, will be well suited for low-power products.