STM8L pk MSP430 Low Power Comparison

My test environment is as follows:

1, external crystal oscillator frequency 1M

2, a 16-bit timer

3, a key interrupt

4, a serial port baud rate: 115200

5, an LED light

6, power supply 3.3V

7. Main program operation: Press key interrupt to print “ STM8L PK MSP430 ” from the serial port. The timer 500MS interrupt will invert the LED.

The above hardware conditions are performed at full speed on the STM8L and MSP430, respectively. Measured currents are compared and results are obtained. Interested friends can try it out.

Discussion instructions:

Low power consumption has always been the focus of major MCU vendors. Recently, a video (STMicroelectronics STM8L low-power series MCU technology demonstration) was very popular on the Internet. ST's engineers used two potatoes, RFID coils, and a cup of hot water to power the STM8L MCU and make the system run normally. This can not help but let me have an interest in the operating power of STM8, in the end how low power STM8L can work? Which module within the MCU has the highest power consumption? How can we reduce the power consumption of STM8L as much as possible?

Let us first look at the data provided by the vendor DS:
1. Operating voltage 1.8V to 3.6V
2. 5 low power modes:

Wait mode

Low power run mode (approximately 5.1uA consumed)

Low power wait mode (approximately 3uA)

AcTIve-halt with full RTC mode (approximately 1.3uA consumed)

Halt mode (approximately 350nA consumed)

Of course, this is just the ideal power consumption provided by the manufacturer. In actual use, different peripherals, different PCB designs, and different software programs will have a significant impact on the power consumption of the system. In the following evaluation, we measured the power consumption in the STM8 RUN mode using the most basic STM8 Discovery development board as a platform. Of course, due to the accuracy of test instruments and the impact of test methods,

Let's first look at how low the STM8-DISCOVERY operating voltage is.

The test circuit is simple, an external regulated power supply, a multimeter connected in series to measure the current, and a multimeter connected in parallel to test the current voltage.

The system does not work when the power supply voltage is 1.8056V, and the LCD on the STM8 board does not light.

When the power supply voltage is 1.8135V, system operation, on-chip program execution, IDD test current is 1.12mA. According to the STM8L user manual (CD00278045 document), we will ampere the current meter into pins 2 and 3 of JP1. The current meter shows 1.08 mA. Basically consistent with IDD measurements. Through this measurement, it can be considered that the operating voltage of STM8 is between 1.80V and 1.81V, basically meeting the 1.8V supply voltage mentioned in the data sheet.

STM8 DS mentioned in: ConsumpTIon: 195 μA/MHz, what does this mean? Is the system clock frequency also related to power consumption?

According to Figure 17 of the user manual, it can be seen that the clock signals used by the STM8 MCU mainly come from four places: HSE (external high-speed crystal), HIS (internal 16M RC oscillator), LSE (external low-speed crystal), and LSI (internal 38KHz low speed) Oscillator). These four clocks are selected by the selector and divided by (1,2,4,8,16,32,64,128) by the system's divider. Because there is no external high-speed crystal oscillator on the board, only the 16 MHz RC oscillator provided inside the chip can be used for testing. In order to better demonstrate the test results, we tested each type of frequency separately. The highest frequency of STM8 is 16MHz, and the lowest frequency is 16/128=125KHZ. The following figures are the current consumption in the RUN mode measured with on-board IDD under various frequency division coefficients. (The test program closed all modules except the ADC module and LCD module and the power supply was 3.3V). The frequency divisions are: 1, 2, 4, 8, 16, 32, 64, 128.

Through testing, we can know that at the same voltage, the current consumed by different operating frequency devices is not the same, but overall it is a downward trend. When this drop is not completely linear, when the system frequency division factor changes from 1 to 2, the effect is obvious. When changing from 8 to 16 and 32, the current consumption of the system has only a slight change, if the frequency division factor of the system changes from 64. Basically, it can be said that there is no change for 128. If there is also a 256-division ratio, the current consumption estimated by the previous rule will not change much. Is this the limit of STM8L? Of course not, as we said before, the STM8 MCU has 4 clock sources. We can use the other three except the external high-speed clock board. The result of our test above is obtained by using the internal 16Mhz RC clock source as the master clock. To make the STM8 operate at a lower frequency, we can select the internal 38k low-speed clock (ie, LSI) as the master clock. When LSI is the main clock and the division factor is 1, the system current consumption varies.