Power Sequencing for Complex Systems

Understanding Power Sequencing in Modern Electronic Systems

As electronic systems grow increasingly complex, the importance of proper power sequencing has become paramount for ensuring reliable operation, preventing component damage, and extending system longevity. Whether you're designing industrial control systems for Nova Scotia's marine sector, developing telecommunications infrastructure across the Maritimes, or creating sophisticated medical devices, understanding and implementing correct power sequencing is essential for professional engineering success.

Power sequencing refers to the controlled, methodical process of turning on and off multiple power supply rails in a specific order, with precise timing relationships. Modern integrated circuits, particularly FPGAs, microprocessors, and complex SoCs, often require multiple voltage rails—sometimes as many as ten or more—each with specific sequencing requirements that must be carefully orchestrated to prevent latch-up conditions, excessive current draw, or permanent damage to sensitive semiconductors.

Why Power Sequencing Matters: Technical Fundamentals

The fundamental reason power sequencing exists stems from the internal structure of modern semiconductors. Most integrated circuits contain multiple power domains, each serving different functional blocks within the chip. When these domains power up in an incorrect order, several problematic conditions can occur:

• Latch-up conditions: When substrate or well voltages are not properly established before I/O voltages are applied, parasitic thyristor structures can trigger, creating low-impedance paths that draw excessive current and potentially destroy the device.

• Contention and crow-bar currents: Improper sequencing can cause output drivers to fight against each other or against external circuits, resulting in current spikes that can exceed 10-15 amperes in severe cases.

• Electromigration damage: Excessive current density during improper power-up can accelerate metal migration in interconnects, reducing long-term reliability.

• Undefined logic states: Without proper sequencing, flip-flops and registers may power up in random states, causing unpredictable system behaviour that can be difficult to diagnose.

For Atlantic Canadian industries relying on electronic systems in harsh environments—such as offshore energy platforms, fishing vessel navigation systems, or pulp and paper mill automation—these reliability concerns are amplified by challenging operating conditions including temperature extremes, humidity, and vibration.

Common Sequencing Requirements

Most modern processors and FPGAs specify sequencing requirements in one of three general patterns. The first, and most common, requires core voltage rails to be established before I/O voltages. For example, a typical FPGA might require its 0.9V core supply to reach 90% of nominal before its 1.8V auxiliary and 3.3V I/O supplies begin ramping. The second pattern involves simultaneous ramp-up, where all rails must track together within a specified voltage window—typically ±300mV. The third pattern involves specific timing delays between rails, often requiring 10-50 milliseconds between successive power rail activation.

Power Sequencing Architectures and Implementation Strategies

Engineers have several architectural approaches available for implementing robust power sequencing. The selection depends on system complexity, cost constraints, and reliability requirements specific to the application.

Discrete Sequencing Solutions

For simpler systems with three to four power rails, discrete sequencing using voltage supervisors, comparators, and enable signal cascading remains a cost-effective approach. A typical implementation might use a supervisory IC like the Texas Instruments TPS3808 or Analog Devices ADM6315 to monitor each rail and generate enable signals for subsequent supplies. This approach offers flexibility but requires careful attention to timing margins and proper hysteresis to prevent oscillation during power transitions.

Component selection for discrete solutions should account for the operating temperature range common in Maritime applications. With ambient temperatures in industrial facilities ranging from -20°C in unheated equipment shelters during winter to +45°C in summer heat, specifying industrial-grade (-40°C to +85°C) or automotive-grade (-40°C to +125°C) components is essential for long-term reliability.

Integrated Power Management Solutions

Complex systems benefit from integrated power management ICs (PMICs) that combine multiple voltage regulators with built-in sequencing logic. Devices such as the Maxim MAX20812 or the Texas Instruments TPS65086 integrate four to eight programmable power rails with configurable sequencing, timing, and fault monitoring in a single package. These solutions reduce board space, simplify design, and provide consistent behaviour across production units.

PMICs typically offer programmable delay times from 250 microseconds to several hundred milliseconds, with sequencing configuration stored in internal registers or programmed via I²C interface. For high-reliability applications, one-time programmable (OTP) variants allow permanent configuration storage, eliminating the risk of sequencing corruption due to software errors or electromagnetic interference.

FPGA-Based Sequencing Controllers

For systems requiring maximum flexibility, small CPLDs or low-cost FPGAs can implement sophisticated sequencing algorithms with features impossible in discrete or PMIC-based solutions. A sequencing controller implemented in a Lattice MachXO3 or Intel MAX 10 FPGA can provide:

• Adaptive timing that adjusts based on temperature or supply characteristics

• Comprehensive telemetry logging for failure analysis

• Integration with system-level health monitoring and predictive maintenance systems

• Hot-swap support with controlled charge management for bulk capacitance

• Soft-start coordination across multiple current-limited supplies

Design Considerations for Robust Power Sequencing

Implementing reliable power sequencing requires attention to several critical design factors beyond basic sequencing order and timing.

Soft-Start and Inrush Current Management

Each power rail must manage its inrush current during startup to prevent excessive stress on upstream supplies and distribution networks. A properly designed soft-start circuit limits capacitor charging current to manageable levels—typically 100-500mA per rail for board-level supplies. The total system inrush must be analysed to ensure compatibility with facility power distribution, particularly important in remote Nova Scotia installations where utility capacity may be limited.

For a system with 10,000µF of bulk capacitance on a 12V rail, uncontrolled inrush could theoretically exceed 100 amperes. Implementing a 2ms soft-start time limits peak current to approximately 60 amperes, while a 10ms soft-start reduces this to roughly 12 amperes—far more manageable for input protection devices and upstream regulators.

Power-Down Sequencing

While power-up sequencing receives significant attention, proper power-down sequencing is equally important for system reliability. Many devices specify reverse sequencing requirements, where I/O supplies must fall before core supplies to prevent damage during shutdown. This is particularly critical in systems with large energy storage elements or in applications where controlled shutdown is required for data integrity.

Implementing controlled power-down requires either active sequencing during shutdown or careful selection of bulk capacitance values to ensure natural discharge follows the correct sequence. A common approach uses larger output capacitors on rails that should decay last, combined with controlled enable signal release during intentional shutdowns.

Fault Detection and Recovery

Professional-grade power sequencing implementations include comprehensive fault detection and recovery mechanisms. Key monitored parameters include:

• Undervoltage: Detection when any rail falls below 90-95% of nominal, triggering protective shutdown

• Overvoltage: Monitoring for rails exceeding 105-110% of nominal due to regulator failure or load transients

• Sequencing timeout: Detection when rails fail to reach proper voltage within expected timeframes, typically 100-500ms

• Thermal monitoring: Integration with temperature sensors on critical regulators and loads

• Current limiting: Detection of overcurrent conditions indicating potential short circuits or component failures

The response to detected faults should be carefully engineered. Immediate shutdown protects hardware but may not be appropriate for all applications. Systems controlling critical Maritime infrastructure—harbour navigation aids, emergency communication systems, or environmental monitoring stations—may require fault ride-through capability or graceful degradation rather than immediate shutdown.

Practical Applications in Atlantic Canadian Industries

Power sequencing requirements manifest differently across the diverse industries served by engineering firms in the Maritime region.

Marine and Offshore Systems

Electronic systems aboard vessels and offshore platforms face unique challenges including wide input voltage variations (typically 18-32VDC from vessel power systems), significant transient events during engine starting or load switching, and the need for rapid restart after momentary power interruptions. Power sequencing designs for these applications often incorporate input energy storage sufficient for 50-100ms ride-through, combined with fast-restart capability that can complete full sequencing within 200-500ms of input power restoration.

Industrial Automation and Process Control

Nova Scotia's manufacturing sector, including food processing, forestry products, and advanced manufacturing, relies on sophisticated automation systems where power sequencing affects both equipment protection and process safety. These systems typically require coordinated sequencing across multiple chassis and subsystems, with interlocks ensuring that actuators cannot energise until control systems are fully operational. Sequencing delays of 2-5 seconds between logic power and actuator power are common requirements.

Telecommunications Infrastructure

Rural connectivity initiatives across Atlantic Canada depend on telecommunications equipment that must operate reliably for years with minimal maintenance. Power sequencing in these applications emphasises robustness against input transients from backup battery systems, solar charge controllers, or small wind generators common in off-grid installations. The sequencing controller itself must be designed for extremely low quiescent current—often below 100µA—to minimise impact on battery-powered standby operation.

Testing and Validation Methodologies

Thorough testing is essential to verify that power sequencing performs correctly across all operating conditions. A comprehensive validation programme should include:

• Oscilloscope verification: Capture of all power rails during startup and shutdown at multiple input voltages and temperatures, verifying timing relationships against specifications

• Margin testing: Operation at voltage extremes (±10% input voltage) and temperature extremes to verify adequate design margins

• Fault injection: Controlled introduction of fault conditions including shorted rails, open connections, and upstream supply failures to verify protection response

• Cycle testing: Extended power cycling tests (minimum 10,000 cycles) to identify infant mortality failures and verify long-term reliability

• EMC susceptibility: Verification that sequencing operates correctly in the presence of conducted and radiated interference at levels specified by applicable standards

Emerging Trends and Future Considerations

The power sequencing landscape continues to evolve with semiconductor technology advances. Systems-on-chip now commonly integrate eight or more power domains, with some advanced processors requiring more than fifteen distinct supply rails. This complexity drives adoption of digital power management architectures using PMBus communication for sequencing control, enabling software-defined power management that can adapt to different operating modes or system configurations.

Additionally, the growing emphasis on energy efficiency has introduced new sequencing considerations around dynamic voltage scaling and power gating. Modern systems may need to sequence power rails not just at startup, but repeatedly during normal operation as processors enter and exit low-power states. These dynamic sequencing events must complete within microseconds rather than milliseconds, requiring careful co-design of power delivery networks and sequencing logic.

Partner with Sangster Engineering Ltd. for Your Power System Design

Implementing reliable power sequencing requires deep understanding of semiconductor requirements, careful circuit design, and thorough validation—expertise that comes from years of hands-on engineering experience. At Sangster Engineering Ltd., our team brings comprehensive electronics engineering capabilities to clients throughout Nova Scotia, Atlantic Canada, and beyond.

Whether you're developing new products requiring complex multi-rail power systems, upgrading existing equipment for improved reliability, or troubleshooting sequencing-related failures in deployed systems, our engineers can provide the technical expertise your project demands. From initial specification development through prototype validation and production support, we deliver professional engineering services that meet the rigorous requirements of industrial, marine, and commercial applications.

Contact Sangster Engineering Ltd. today to discuss your power system design challenges. Our Amherst, Nova Scotia facility is ideally positioned to serve clients across the Maritime provinces, and we welcome the opportunity to apply our expertise to your most demanding engineering projects.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.