MCU Clock Slewing to Limit Startup Current Transients
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Solution Overview
Problem
Existing electronic devices with micro-controller units (MCUs) face significant current transients during startup, leading to operation outside desired specifications and requiring over-designed power supply circuits to manage these surges, which are inefficient and costly.
Innovation Solution
The MCU controls its own current supply by gradually increasing its clock frequency during startup, acting as an intelligent load to manage the current drawn from the voltage regulator, using mechanisms like intermittent steps, pulse width modulation, and hardware slewing to avoid sudden current spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the MCU starts up at maximum frequency immediately, then the startup time is minimized, but a large current transient is generated causing operation outside specifications
Solution Approach 1:
The system performs preliminary actions by initially operating the MCU at a conservative frequency before transitioning to maximum frequency. The boot loader runs at a reduced frequency to safely initialize the system and establish the PLL, preventing current transients during the critical startup phase while still achieving eventual maximum performance.
Solution Approach 2:
The system dynamically adjusts the operating frequency of the MCU during startup. The frequency transitions from a conservative initial value to the maximum operating frequency as the system stabilizes. This dynamic frequency adjustment allows the system to balance startup time requirements with current transient constraints.
2Reliability
If the power supply is over-designed to handle current surges, then the voltage remains within specifications during startup, but the power supply circuit becomes more expensive and space-consuming
Solution Approach 1:
The MCU serves itself by implementing frequency control during startup to manage current draw. Instead of requiring an externally over-designed power supply, the MCU autonomously adjusts its operating frequency to keep current within the power supply's capabilities, eliminating the need for expensive decoupling capacitors and robust power supply circuitry.
3Speed
If the voltage regulator is made faster to catch up with sudden current demands, then the current supply responds quickly, but the regulator becomes more expensive and complex
Solution Approach 1:
The system applies preliminary anti-action by preemptively reducing the MCU frequency when current demand increases. Instead of trying to make the voltage regulator faster to handle sudden current demands, the system prevents the current surge from occurring in the first place by operating at a conservative frequency during startup, eliminating the need for a high-speed, complex voltage regulator.
Data Source
AI summary
An electronic device comprises a voltage regulator supplying a current to a load such as a micro-controller unit. The load controls the current provided to the load from the voltage regulator. Preferably, the load controls the level of current supplied to the load upon start-up, thereby avoiding power surges being drawn by the load.