LTC4257
IEEE 802.3af PD
Power over Ethernet
Interface Controller
FEATURES
DESCRIPTIO
Complete Power Interface Port for IEEE 802.3af The LTC 4257 provides complete signature and power
Powered Devices (PDs) interface functions for a device operating in an IEEE
Onboard 100V, 400mA Power MOSFET 802.3af Power over Ethernet (PoE) system. The LTC4257
Precision Input Current Limit simplifies Powered Device (PD) design by incorporating
Onboard 25k Signature Resistor the 25k signature resistor, the classification current source,
Programmable Classification Current (Class 0-4) input current limit with thermal foldback, undervoltage
Undervoltage Lockout lockout and power good signalling, all in a single 8-pin
Smart Thermal Protection package. By incorporating a high voltage power MOSFET
Power Good Signal onboard, the LTC4257 provides the system designer with
Available in 8-Pin SO and Low Profile (3mm 3mm) reduced cost while also saving board space.
DFN Packages
The LTC4257 can interface directly with a variety of Linear
Technology DC/DC converter products to provide a cost
U
effective power solution for IP phones, wireless access
APPLICATIO S
points and other PDs. Linear Technology also provides
IP Phone Power Management
solutions for Power Sourcing Equipment (PSE) applica-
Wireless Access Points
tions with quad network power controllers.
Telecom Power Control
The LTC4257 is available in the 8-pin SO and low profile
(3mm 3mm) DFN packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
LTC4257 Charging 300F
Load Capacitor
Powered Device (PD) V
IN
50V/DIV
LTC4257 V
V OUT
IN
GND
~ + SMAJ58A
20V/DIV
48V FROM
+
SWITCHING
5F
POWER SOURCING R
CLASS
0.1F 100k
DF01SA POWER SUPPLY
MIN
EQUIPMENT
+
(PSE)
PWRGD SHDN I
IN
3.3V
~ R
CLASS RTN 200mA/DIV
TO LOGIC
V V
IN OUT
4257 TA01
PWRGD
50V/DIV
5ms/DIV 4225 TA02
4257fb
1
U
ULTC4257
ABSOLUTE AXI U RATI GS
(Notes 1, 2)
Operating Ambient Temperature Range
V Voltage ............................................. 0.3V to 100V
IN
LTC4257C ............................................... 0C to 70C
V , PWRGD Voltage ............. V + 100V to V 0.3V
OUT IN IN
LTC4257I............................................. 40C to 85C
R Voltage ............................ V + 7V to V 0.3V
CLASS IN IN
Storage Temperature Range
PWRGD Current .................................................. 10mA
S8 Package....................................... 65C to 150C
R Current .................................................. 100mA
CLASS
DD Package ...................................... 65C to 125C
Lead Temperature (Soldering, 10 sec).................. 300C
UUW
PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
NC 1 8 GND
R 2 7 NC
NC 1 8 GND CLASS
NC 3 6 PWRGD
R 2 7 NC
CLASS
V 4 5 V
IN OUT
NC 3 6 PWRGD
V 4 5 V
IN OUT
DD PACKAGE
8-LEAD (3mm 3mm) PLASTIC DFN
S8 PACKAGE
8-LEAD PLASTIC SO T = 125C, = 43C/W
JMAX JA
T = 150C, = 150C/W EXPOSED PAD TO BE SOLDERED TO
JMAX JA
ELECTRICALLY ISOLATED PCB HEATSINK
ORDER PART NUMBER S8 PART MARKING
ORDER PART NUMBER DD PART MARKING*
LTC4257CS8 4257 LTC4257CDD LACT
LTC4257IS8 4257I LTC4257IDD
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF
Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: