13. PTC Fuse for USB Port Protection

If a faulty USB device creates a short circuit, the full supply current rushes through the port. This can burn PCB traces, damage the USB host IC, or even melt the connector.

A PTC (Positive Temperature Coefficient) resettable fuse in series with the 5V output changes from low resistance to very high resistance when current exceeds its trip threshold. This effectively disconnects the faulty port. When the fault is removed, the PTC cools down and resets automatically.

Hold Current Selection:

USB port supplies 500mA. PTC fuses derate with temperature (typically 25–50% at +85°C). Hold current range: 500mA to 750mA. Below 500mA = nuisance tripping. Above 750mA = insufficient protection.

Required: Polymeric · Ih 500–750mA · ≥6V · Imax ≥5A · 1210 · SMD · Littelfuse

Go to DigiKey.com → Circuit Protection → PTC Resettable Fuses

Apply these filters:

• Current - Hold (Ih) → 500mA to 750mA range
• Voltage - Max → 6V or higher
• Package / Case → 1210
• Mounting Type → Surface Mount
• Manufacturer → Littelfuse Inc.
• Part Status → Active

Tip: PTC fuses have two key currents: Hold current (Ih) = max current where it stays conducting. Trip current (It) = min current where it trips. It is typically ~2× Ih.

The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?

Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide

➡ View Matching Parts — Littelfuse, PTC, Ih 500–750mA, ≥6V, 1210 SMD