PPTC Fuse for USB Port Protection

Question

Problem: PPTC Fuse for USB Port Protection. Solve this hands-on electronics task on EWskills.

Accepted Answer

1. Component Purpose & Calculation

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

2. How to Find It on DigiKey

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.

3. Key Specifications & What They Mean

Specification	Required	Why
Type	Polymeric	Standard resettable PTC technology.
Hold Current	500–750mA	Holds at 500mA; trips on overload.
Voltage Max	≥6V	Must exceed 5V USB rail.
Current Max	≥5A	Survives short-circuit fault current.
Package	1210 SMD	Compact for USB port PCB area.
Manufacturer	Littelfuse	Company AVL requirement.
Temp Range	−40°C to +85°C	Standard operating range.
RoHS	Yes	Compliance required.

4. Selecting a Safe, Production-Ready Part

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

5. Filtered DigiKey Link

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

13. PPTC Fuse for USB Port Protection