Microcontroller power management method - Power Circuit - Circuit Diagram

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Nuvoton's NUC1xx series includes NUC101, NUC100, NUC120, NUC130, and NUC140. These are 32-bit microcontrollers (MCUs) featuring the ARM Cortex-M0 core. Depending on the clock settings, they can operate at frequencies up to 50 MHz. However, when performing simple tasks or under light system loads, the CPU doesn’t need to run at its maximum clock speed. In such cases, you can adjust the system clock to reduce the frequency, which helps save power.

Another way to save power is by putting the CPU into Idle or Power Down modes when it’s waiting for further instructions or only needs to operate occasionally. When needed, it can be easily awakened to handle tasks. Additionally, unused system modules can also be switched off to avoid unnecessary power usage. This article explores these power-saving strategies and provides practical examples to illustrate their implementation.

Switching System Modules

In the Nuvoton NUC1xx series, individual system modules can be disabled when not in use by cutting off their clock inputs. This effectively puts them into an off state, conserving energy. Nearly all modules within the NUC1xx series can be independently powered down. These include the Watchdog Timer, RTC, Timers 0-3, I2C0-1, SPI0-3, UART0-2, PWM0-7, CAN, USB, ADC, ACMP, PS/2, PDMA, and Flash ISP. However, not all modules are available across every variant; for instance, the CAN module is present only in NUC130 and NUC140. For detailed information about each chip, consult the corresponding datasheets.

The power consumption associated with each module is outlined in Table 1:

Nuvoton achieves power savings in the NUC1xx series by disabling individual modules through the deactivation of their respective clocks. To shut down a particular module, its corresponding clock control register must be configured accordingly. The NUC1xx offers the AHBCLK and APBCLK registers to manage the enabling/disabling of these modules.

System Clock Settings

The power consumption of Nuvoton’s NUC1xx directly correlates with its operational clock speed. Higher clock speeds lead to greater power usage, while lower speeds offer better energy efficiency but may limit processing capacity. Thus, balancing computational demands with energy conservation requires adjusting the CPU’s clock based on real-time requirements to optimize performance.

The NUC1xx integrates a PLL that generates the necessary system clock from either an external 12 MHz crystal or an internal 22 MHz oscillator. The output from the PLL can serve as the CPU’s operating frequency after appropriate frequency division. Furthermore, the NUC1xx allows direct connection of the CPU’s operating frequency via an external 32 kHz crystal or an internal 10 kHz oscillator. This design provides significant flexibility in configuring the CPU’s clock.