16. PPTC Resettable Fuse for PoE Ethernet Port Protection
1. Component Purpose
PoE supplies up to 57V through the Ethernet cable. If a fault occurs on the board’s PoE input, the high voltage can drive dangerous current levels. A PTC fuse limits this by tripping on overcurrent.
The critical requirement is voltage rating ≥60V. Standard 1210 PTC fuses max out at ~30V. A 1812 package is required because it supports higher voltage ratings suitable for PoE.
Hold Current: Device draws 350mA. With derating: Ih = 450mA to 700mA
Required: Polymeric · Ih 450–700mA · ≥60V · Imax ≥5A · 1812 · SMD · Littelfuse
2. How to Find It on DigiKey
Go to DigiKey.com → Circuit Protection → PTC Resettable Fuses
Apply these filters:
- Current - Hold (Ih) → 450mA to 700mA range
- Voltage - Max → 60V or higher
- Package / Case → 1812
- Mounting Type → Surface Mount
- Manufacturer → Littelfuse Inc.
- Part Status → Active
Important: Do not use a 1210 PTC fuse for PoE. Most 1210 PTCs are rated ≤30V — far below the 57V PoE supply. The 1812 package is required for the higher voltage rating.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Type | Polymeric | Standard resettable PTC. |
| Hold Current | 450–700mA | 350mA load + thermal derating. |
| Voltage Max | ≥60V | PoE max is 57V; needs margin. |
| Current Max | ≥5A | Survives PoE fault current. |
| Package | 1812 SMD | Required for ≥60V voltage rating. |
| 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