DocumentationDatasheet
Reliability Data
- PoE Consortium Clause # 33 Parametric Report
- PoE Consortium Interoperability Report
- R413 Reliability Data
Product Selector Card
cad_symbol
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
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.
3x3 DFN-8,SO-8
Package Variations and Pricing
| Part Number | Package | Pins | Temp | Price (1-99) |
Price (1k)* |
|---|---|---|---|---|---|
| LTC4257CDD#PBF | DFN | 8 | C | $2.41 | $1.70 |
| LTC4257CDD#TRPBF | DFN | 8 | C | $1.76 | |
| LTC4257CDD-1#PBF | DFN | 8 | C | $2.59 | $1.85 |
| LTC4257CDD-1#TRPBF | DFN | 8 | C | $1.91 | |
| LTC4257CS8#PBF | SO | 8 | C | $2.32 | $1.65 |
| LTC4257CS8#TRPBF | SO | 8 | C | $1.71 | |
| LTC4257CS8-1#PBF | SO | 8 | C | $2.50 | $1.75 |
| LTC4257CS8-1#TRPBF | SO | 8 | C | $1.81 | |
| LTC4257IDD#PBF | DFN | 8 | I | $2.77 | $1.95 |
| LTC4257IDD#TRPBF | DFN | 8 | I | $2.01 | |
| LTC4257IDD-1#PBF | DFN | 8 | I | $2.95 | $2.10 |
| LTC4257IDD-1#TRPBF | DFN | 8 | I | $2.16 | |
| LTC4257IS8#PBF | SO | 8 | I | $2.68 | $1.90 |
| LTC4257IS8#TRPBF | SO | 8 | I | $1.96 | |
| LTC4257IS8-1#PBF | SO | 8 | I | $2.86 | $2.00 |
| LTC4257IS8-1#TRPBF | SO | 8 | I | $2.06 | |
| LTC4257CS8 | SO | 8 | C | $4.64 | $3.30 |
| LTC4257CS8#TR | SO | 8 | C | $3.42 | |
| LTC4257IS8 | SO | 8 | I | $5.36 | $3.80 |
| LTC4257IS8#TR | SO | 8 | I | $3.92 | |
| LTC4257CS8-1 | SO | 8 | C | $5.00 | $3.50 |
| LTC4257CS8-1#TR | SO | 8 | C | $3.62 | |
| LTC4257IS8-1 | SO | 8 | I | $5.72 | $4.00 |
| LTC4257IS8-1#TR | SO | 8 | I | $4.12 | |
| LTC4257CDD-1 | DFN | 8 | C | $5.18 | $3.70 |
| LTC4257CDD-1#TR | DFN | 8 | C | $3.82 | |
| LTC4257IDD-1 | DFN | 8 | I | $5.90 | $4.20 |
| LTC4257IDD-1#TR | DFN | 8 | I | $4.32 | |
| LTC4257CDD | DFN | 8 | C | $4.82 | $3.40 |
| LTC4257CDD#TR | DFN | 8 | C | $3.52 | |
| LTC4257IDD | DFN | 8 | I | $5.54 | $3.90 |
| LTC4257IDD#TR | DFN | 8 | I | $4.02 |
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 |