The power sequencing during startup is a crucial process in microcontrollers (MCUs) to ensure proper operation and prevent issues. Let%27s explore how MCUs handle power sequencing:

1. Why Worry About Power Sequencing?
- Complex MCUs, including microprocessors, FPGAs, DSPs, and system-on-chip (SoC) devices, typically run from multiple voltage rails.
- To prevent problems like lock-ups, bus contention, and high inrush current, designers need to start and shut down these power rails in a specific order.
- This process is known as power sequence control or power sequencing.

2. Voltage Sequencing for Complex ICs:
- Complex ICs (such as FPGAs) internally break down into multiple power domains.
- These domains include:
- Core: The processor and logic foundation of the IC. It operates at low voltage and high current.
- I/O: Represents various inputs and outputs. Voltage levels depend on the interface type.
- Auxiliary Circuitry: Includes noise-sensitive analog circuits (e.g., PLLs). Ripple voltage must be minimized.
- Starting up power supplies for each domain in the incorrect order can cause problems and even damage the IC.

3. Example: FPGA I/O and Core Domains:
- FPGAs typically power the core logic, I/O, and auxiliary circuits separately.
- Proper power-up and power-down sequencing are essential:
- If the I/O domain is powered on before the core, the I/O pins end up in indeterminate states.
- For example, the I/O section relies on transmitting and receiving data on a tristate bus, and its control is handled by the core.

4. Solutions for Effective Power Sequencing:
- Power Sequencers, Monitors, and Supervisors:
- These devices monitor voltage and current levels to calculate power levels.
- They protect complex ICs and subassemblies during ramp-up and shutdown.
- Voltage and Current Monitoring:
- Techniques like monitoring voltage and current help ensure safe power-up and power-down.
- Proper Timing and Sequencing:
- Designers must adhere to specified power rail timing and sequencing to avoid issues.

In summary, power sequencing during MCU startup involves careful management of voltage domains to prevent problems and ensure reliable operation¹.


(1) Controlling Startup and Shutdown Power Sequences | DigiKey. https://www.digikey.com/en/articles/controlling-startup-and-shutdown-power-sequences.
(2) What happens when an MCU powers up? - microcontrollertips.com. https://www.microcontrollertips.com/what-happens-when-an-mcu-powers-up/.
(3) Simple Power Sequencer Using MSP430 MCUs - Texas Instruments India. https://www.ti.com/lit/pdf/slaa829.
(4) Why Is Power Sequencing Needed? | Microchip Technology. https://www.microchip.com/en-us/about/media-center/blog/2022/why-is-power-sequencing-needed.
(5) Modify the startup PWM sequence - STMicroelectronics Community. https://community.st.com/t5/stm32-mcus-motor-control/modify-the-startup-pwm-sequence/td-p/354968.

icDirectory Limited | https://www.icdirectory.com/b/blog/how-do-mcus-handle-power-sequencing-during-startup.html