USB-C 240W Protection: TCO/ESD/TVS Coordinated Design

Why High-Power USB-C Protection Matters Now

USB-C 240W Power Delivery has transformed device charging but introduces critical challenges: cable thermal runaway, connector hot spots, and ESD vulnerability. Coordinating TCO, ESD, and TVS protection is essential for system safety.

Understanding USB-C 240W Power Delivery Fundamentals

USB PD 3.1 EPR enables 240W transfer through USB-C at 28V, 36V, and 48V with 5A current—up from the previous 100W limit. The 24-pin connector must handle high-speed data and high power simultaneously.

Power Distribution in 240W USB-C Systems

USB-C uses bonded VBUS pins for current sharing. At 240W (48V × 5A), contact points experience significant power dissipation. Cable resistance (80-150 milliohms) generates 2-3.75W of heat through I²R losses at 5A.

Thermal Challenges in High-Power USB-C Implementations

Heat Generation Sources

Thermal stress in 240W USB-C systems comes from:

• Contact resistance at interfaces (10-30 milliohms per contact)
• Cable conductor resistance
• Power conversion losses
• Ambient temperature variations

Connector temperatures can reach 70-90°C under continuous 240W operation, approaching UL and IEC safety limits.

Thermal Runaway Risks

Thermal runaway occurs when rising temperature degrades contact quality, increasing resistance and generating more heat. Poor insertion, contamination, or wear can trigger this feedback loop, pushing temperatures above 100°C and risking insulation melting and fire.

TCO Protection Strategy for USB-C Power Systems

What Is TCO and How Does It Work?

TCO devices are temperature-sensitive switches that open circuits at preset thresholds. For USB-C 240W, TCOs typically trigger at 90-100°C before materials degrade.

TCO Placement Considerations

Strategic TCO placement includes:

• Cable-integrated TCOs: Near connector overmold for direct hotspot monitoring
• PCB-mounted TCOs: Adjacent to VBUS traces and controllers
• Connector housing TCOs: Within metal shell for overall thermal detection

TCOs require direct thermal contact with heat sources while maintaining electrical isolation from high-voltage paths.

TCO Response Characteristics

Modern USB-C TCO devices feature:

• Trip temperature accuracy: ±5°C
• Response time: 3-10 seconds
• Hold current: Minimum 6A
• Voltage rating: 60V DC minimum
• Reset options: One-shot or resettable

ESD Protection Requirements for USB-C Interfaces

ESD Threats in USB-C Environments

USB-C connectors face ESD from:

• Human body model (HBM) during hot-plugging
• Machine model (MM) from automated equipment
• Charged device model (CDM)

USB-C requires ±8kV contact and ±15kV air discharge immunity per IEC 61000-4-2. High-speed data lines need minimal-capacitance protection for signal integrity.

ESD Protection Device Selection

USB-C 240W ESD protection requirements:

• VBUS: High-power TVS diodes with 60V+ breakdown and 100A+ surge capability
• CC lines: Low-capacitance TVS arrays (<1pF) for PD communication
• High-speed data: Ultra-low capacitance arrays (<0.3pF) for USB 3.2/4.0
• SBU/auxiliary pins: Medium-capacitance protection for lower-speed signals

TVS Device Coordination with Power Systems

TVS Operating Principles

TVS devices clamp voltage spikes by conducting surge current above their breakdown threshold. For USB-C, they must distinguish between normal operating voltages (up to 48V) and transient over-voltages.

Critical TVS Parameters for 240W USB-C

Standoff voltage (VR): Must exceed maximum operating voltage. For 48V EPR, 58V minimum recommended for ripple and tolerance margins.

Breakdown voltage (VBR): Typically 10-20% above standoff, initiating protection before IC damage.

Clamping voltage (VC): Maximum voltage during surge conduction. Should stay below IC absolute maximums, typically <65V for 48V systems.

Peak pulse current (IPP): Minimum 30A for robust protection, preferably 50-100A for IEC 61000-4-5 Level 4.

Multi-Stage TVS Protection Architecture

Optimal protection uses cascaded stages:

• Primary stage: High-energy TVS at cable entry (100A+ capability)
• Secondary stage: Lower-energy TVS near ICs for precise clamping

Series resistance (1-10Ω) between stages creates voltage division, optimizing each stage’s operation.

Coordinated TCO/ESD/TVS Protection Design

Integration Challenges

Key integration considerations:

• TVS leakage current generates heat, affecting TCO triggering
• TCO placement must avoid ESD paths to prevent false triggering
• PCB layout must minimize TVS parasitic inductance while maintaining TCO thermal zones

Protection Architecture

Layer 1 – Cable/Connector:

• TCO in cable assembly (90-95°C trip)
• Primary TVS at VBUS (60V standoff, 100A IPP)
• ESD arrays on CC/data lines

Layer 2 – PCB Input:

• Secondary TVS post-filtering (58V standoff, 30A IPP)
• PCB TCO monitoring traces (95-100°C trip)
• Current sensing for over-current coordination

Layer 3 – IC Protection:

• Low-capacitance ESD suppressors on controller inputs
• On-chip protection as final defense

PCB Layout Guidelines

• TVS grounding: Low-inductance connections (<10nH) via multiple ground vias
• TCO thermal isolation: Separate thermal zones from other heat sources
• VBUS routing: Wide traces (100mil+ for 5A) with thermal relief at TCO
• Keep-out zones: 5mm clearance between high-voltage TVS and sensitive circuits

Safety Standards and Compliance

UL/IEC Standards

USB-C 240W compliance requirements:

• IEC 62368-1: AV/IT equipment safety
• UL 62368-1: North American safeguarding requirements
• IEC 61000-4-2: ESD immunity (±8kV contact, ±15kV air)
• IEC 61000-4-4: Fast transient/burst immunity
• IEC 61000-4-5: Surge immunity

Temperature Limits

Maximum surface temperatures:

• Frequently touched: 60°C max
• Occasionally touched: 70°C max
• Internal components: 90-100°C with proper materials

TCO ensures limits aren’t exceeded under fault conditions.

USB-IF Certification

240W EPR certification requires:

• USB Type-C Cable/Connector Spec 2.1 compliance
• USB PD 3.1 specification adherence
• Cable temperature rise measurements
• E-Marker functionality validation

Testing and Validation

Thermal Testing

Temperature rise: Measure at 240W for 2+ hours in 25°C ambient. Max rise: 45°C (70°C absolute).

TCO functional: Verify triggering at specified temperatures. Circuit opens in 3-10 seconds.

Thermal cycling: 1000+ cycles of 0-240W transitions for contact stability.

ESD and Surge Testing

Contact discharge (IEC 61000-4-2): ±8kV to accessible parts. System must function or auto-recover.

Surge testing (IEC 61000-4-5): Apply surge waveforms, verify TVS clamping and system survival.

Repetitive pulse: TVS maintains clamping after 1000+ pulses at rated current.

Combined Stress Testing

Advanced testing includes:

• ESD at elevated temperatures (60-70°C)
• Surge during high-power operation
• Connector cycles under load
• Contamination/humidity with electrical testing

Component Selection

TCO Selection

• Trip temperature: 90-100°C (cable/connector), 85-95°C (PCB)
• Hold current: 6A minimum, 7-8A preferred
• Voltage: 60V DC minimum, 72V preferred
• Package: 3-5mm diameter for cable integration
• Reset: Non-resettable (consumer), resettable (industrial)

TVS Selection

• Standoff: 58V minimum for 48V systems
• Peak current: 50-100A (primary), 30A (secondary)
• Clamping: <65V at rated current
• Capacitance: Not critical for VBUS, <1pF for CC, <0.3pF for data
• Package: SMT with adequate thermal performance

ESD Array Selection

• USB 3.2/4.0: <0.3pF, ±8kV minimum
• CC lines: <1pF, 10V rating, ±8kV
• SBU: <5pF acceptable, ±8kV

Common Design Mistakes

Inadequate Current Sharing

Problem: Uneven current distribution across VBUS pins creates hotspots.

Solution: Kelvin sensing or symmetrical PCB routing. Use quality connectors with tight resistance tolerances.

Wrong TVS Voltage Range

Problem: Standoff too close to operating voltage causes premature conduction.

Solution: Select standoff ≥20% above max operating voltage.

TCO False Triggering

Problem: TCO triggers during normal operation.

Solution: Thorough thermal analysis. Isolate TCO from unrelated heat sources.

Insufficient CC Line Protection

Problem: CC lines lack ESD protection, causing field failures.

Solution: Always use low-capacitance (<1pF) ESD protection on CC lines.

Future Trends

Active Protection

• Temperature monitoring ICs for predictive maintenance
• Programmable current limiting with thermal coordination
• ML algorithms predicting thermal runaway

Integration Trends

• Combined TVS/ESD arrays in single packages
• TCO with integrated temperature sensing
• PD controllers with built-in over-temperature protection

Higher Power Levels

Future systems require:

• Higher current-rated TCO devices
• Greater surge capability TVS
• Advanced thermal management with active cooling

Implementation Example

240W Laptop Charger Protection

Specifications:

• Output: 5V/3A to 48V/5A (EPR)
• Cable: USB-C, E-Marker, 2m

Cable assembly:

• TCO: 95°C trip, 6A hold, 72V
• Primary TVS: 58V standoff, 100A IPP
• ESD arrays: CC (<1pF, ±8kV), data (<0.35pF, ±8kV)

Charger PCB:

• Input TVS: 58V standoff, 30A IPP
• PCB TCO: 100°C trip, 8A hold
• Current sense: 5mΩ resistor
• PD controller with temperature monitoring

Layout:

• VBUS: 120mil traces on 2oz copper
• TVS ground: 4× 12mil vias to ground plane
• TCO: 3mm from VBUS, thermal vias below

Conclusion

USB-C 240W requires coordinated thermal, over-voltage, and ESD protection. TCO provides thermal protection, TVS guards against transients, and ESD protection ensures signal integrity and IC survival.

Success demands careful component selection, PCB layout, thermal management, and safety compliance. As power levels increase, protection design becomes increasingly critical.

Engineers must view TCO, ESD, and TVS as an integrated system. Through proper design, testing, and validation, USB-C 240W systems deliver high power while maintaining safety and reliability.