LTC4257-1 - IEEE 802.3af PD Power over Ethernet Interface Controller with Dual Current Limit
Features
- Complete Power Interface Port for IEEE 802.3af Powered Devices (PDs)
- Onboard 100V, 400mA Power MOSFET
- Precision Dual Level Current Limit
- Onboard 25k Signature Resistor with Disable
- Programmable Classification Current (Class 0-4)
- Undervoltage Lockout
- Thermal Overload Protection
- Power Good Signal
- Available in 8-Pin SO and Low Profile (3mm x 3mm) DFN Packages
AEC-Q100 data available for specific packages
Typical Application
Description
The LTC4257-1 provides complete signature and power interface functions for a device operating in an IEEE 802.3af Power over Ethernet (PoE) system. The LTC4257-1 simplifies Powered Device (PD) design by incorporating the 25k signature resistor, classification current source, input current limit, undervoltage lockout, thermal overload protection, signature disable and power good signalling, all in a single 8-pin package. The LTC4257-1 includes a precision, dual level current limit circuit. This allows it to charge large load capacitors and interface with legacy Power over Ethernet systems while maintaining compatibility with the current IEEE 802.3af specification. By incorporating a high voltage power MOSFET onboard, the LTC4257-1 provides the system designer with reduced cost while also saving board space.
The LTC4257-1 can interface directly with a variety of Linear Technology DC/DC converter products to provide a cost effective power solution for IP phones, wireless access points and other PDs. Linear Technology also provides network power controllers for Power Sourcing Equipment (PSE) applications.
The LTC4257-1 is available in the 8-pin SO and low profile (3mm x 3mm) DFN packages.
Packaging
CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.
For complete and up to date package information and drawings, please refer to our packaging page
| Part Number | Package | Code | Temp | Package Drawing |
RoHS |
|---|---|---|---|---|---|
| LTC4257CDD-1#PBF | 3x3 DFN-8 | DD | C | 05-08-1698 | Yes |
| LTC4257CDD-1#TRPBF | 3x3 DFN-8 | DD | C | 05-08-1698 | Yes |
| LTC4257CS8-1#PBF | SO-8 | S8 | C | 05-08-1610 (S8) | Yes |
| LTC4257CS8-1#TRPBF | SO-8 | S8 | C | 05-08-1610 (S8) | Yes |
| LTC4257IDD-1#PBF | 3x3 DFN-8 | DD | I | 05-08-1698 | Yes |
| LTC4257IDD-1#TRPBF | 3x3 DFN-8 | DD | I | 05-08-1698 | Yes |
| LTC4257IS8-1#PBF | SO-8 | S8 | I | 05-08-1610 (S8) | Yes |
| LTC4257IS8-1#TRPBF | SO-8 | S8 | I | 05-08-1610 (S8) | Yes |
Order Info
- Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
- Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
- Please refer to our general ordering information or the product datasheet for more details
Package Variations and Pricing
| Part Number | Package | Temp | Price (1-99) |
Price (1k)* |
RoHS | |
|---|---|---|---|---|---|---|
| LTC4257CDD-1#PBF | 3x3 DFN-8 | C | $2.59 | $1.85 | Yes | |
| LTC4257CDD-1#TRPBF | 3x3 DFN-8 | C | $1.91 | Yes | ||
| LTC4257CS8-1#PBF | SO-8 | C | $2.50 | $1.75 | Yes | |
| LTC4257CS8-1#TRPBF | SO-8 | C | $1.81 | Yes | ||
| LTC4257IDD-1#PBF | 3x3 DFN-8 | I | $2.95 | $2.10 | Yes | |
| LTC4257IDD-1#TRPBF | 3x3 DFN-8 | I | $2.16 | Yes | ||
| LTC4257IS8-1#PBF | SO-8 | I | $2.86 | $2.00 | Yes | |
| LTC4257IS8-1#TRPBF | SO-8 | I | $2.06 | Yes | ||
| Buy Now • Request Samples | ||||||
Demo Boards
Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.| Part Number | Description | Price | Documentation |
|---|---|---|---|
| DC671A | LTC4257CS8-1 | Power-Over-Ethernet Interface Controller, Vsig = 48V, Vout = 3.3V | $75.00 | |
| Buy Now | |||
Designed for Automotive and Transportation Applications
AEC-Q100 data is available for these specific part numbers. Please contact your local sales representative for more information regarding reliability reports or to inquire about parts that are not included. For more information, view our Automotive and Transportation page
| Part Number | Package | Temp | Price (1-99) |
Price (1k)* |
RoHS | |
|---|---|---|---|---|---|---|
| LTC4257IDD-1#PBF | 3x3 DFN-8 | I | $2.95 | $2.10 | Yes | |
| LTC4257IDD-1#TRPBF | 3x3 DFN-8 | I | $2.16 | Yes | ||
| Buy Now • Request Samples | ||||||
Applications
- IP Phone Power Management
- Wireless Access Points
- Telecom Power Control
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Design Tools
LTspice
LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice
Models for the following parts are available in LTspice:
LTC4257
LTC4257-1
Technical Support
- For immediate technical assistance, contact your local sales office or distributor or call 1-800-4-LINEAR (US customers only) or 408-432-1900.
- For less urgent requests, please complete our Technical Support Request Form. Please allow 2-3 business days for reply.
