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Linear Technology Electronic Components Datasheet

LTC4257IS8 Datasheet

IEEE 802.3af PD Power over Ethernet Interface Controller

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LTC4257
IEEE 802.3af PD
Power over Ethernet
Interface Controller
FEATURES
Complete Power Interface Port for IEEE 802.3af®
Powered Devices (PDs)
Onboard 100V, 400mA Power MOSFET
Precision Input Current Limit
Onboard 25k Signature Resistor
Programmable Classification Current (Class 0-4)
Undervoltage Lockout
Smart Thermal Protection
Power Good Signal
Available in 8-Pin SO and Low Profile (3mm × 3mm)
DFN Packages
U
APPLICATIO S
IP Phone Power Management
Wireless Access Points
Telecom Power Control
DESCRIPTIO
The LTC®4257 provides complete signature and power
interface functions for a device operating in an IEEE
802.3af Power over Ethernet (PoE) system. The LTC4257
simplifies Powered Device (PD) design by incorporating
the 25k signature resistor, the classification current source,
input current limit with thermal foldback, undervoltage
lockout and power good signalling, all in a single 8-pin
package. By incorporating a high voltage power MOSFET
onboard, the LTC4257 provides the system designer with
reduced cost while also saving board space.
The LTC4257 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
solutions for Power Sourcing Equipment (PSE) applica-
tions with quad network power controllers.
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
–48V FROM
POWER SOURCING
EQUIPMENT
(PSE)
~+
DF01SA 0.1µF
~–
Powered Device (PD)
SMAJ58A
LTC4257
GND
RCLASS
100k
RCLASS
PWRGD
5µF +
MIN
VIN
VOUT
VIN
SWITCHING
POWER SUPPLY
SHDN
RTN
+
3.3V
TO LOGIC
4257 TA01
LTC4257 Charging 300µF
Load Capacitor
VIN
50V/DIV
VOUT
20V/DIV
IIN
200mA/DIV
PWRGD
50V/DIV
5ms/DIV
4225 TA02
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Linear Technology Electronic Components Datasheet

LTC4257IS8 Datasheet

IEEE 802.3af PD Power over Ethernet Interface Controller

No Preview Available !

LTC4257 www.DataSheet4U.com
ABSOLUTE AXI U RATI GS
(Notes 1, 2)
VIN Voltage ............................................. 0.3V to – 100V
VOUT, PWRGD Voltage ............. VIN + 100V to VIN – 0.3V
RCLASS Voltage ............................ VIN + 7V to VIN – 0.3V
PWRGD Current .................................................. 10mA
RCLASS Current .................................................. 100mA
UW U
PACKAGE/ORDER I FOR ATIO
Operating Ambient Temperature Range
LTC4257C ............................................... 0°C to 70°C
LTC4257I ............................................. –40°C to 85°C
Storage Temperature Range
S8 Package ....................................... – 65°C to 150°C
DD Package ...................................... – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
NC 1
RCLASS 2
NC 3
VIN 4
8 GND
7 NC
6 PWRGD
5 VOUT
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 150°C/W
TOP VIEW
NC 1
RCLASS 2
NC 3
VIN 4
8 GND
7 NC
6 PWRGD
5 VOUT
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD TO BE SOLDERED TO
ELECTRICALLY ISOLATED PCB HEATSINK
ORDER PART NUMBER
S8 PART MARKING ORDER PART NUMBER DD PART MARKING*
LTC4257CS8
LTC4257IS8
4257
4257I
LTC4257CDD
LTC4257IDD
LACT
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF
Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grades are identified by a label on the shipping container.
ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
VIN
IIN_ON
IIN_CLASS
ICLASS
PARAMETER
CONDITIONS
Supply Voltage
Maximum Operating Voltage
Signature Range
Classification Range
UVLO Turn-On Voltage
UVLO Turn-Off Voltage
Voltage with Respect to GND Pin (Notes 4, 5, 6)
IC Supply Current when ON
VIN = – 48V, Pins 5, 6 Floating
IC Supply Current During Classification VIN = – 17.5V, Pin 2 Floating, VOUT Tied to GND
(Note 7)
Current Accuracy During Classification 10mA < ICLASS < 40mA, – 12.5V VIN – 21V,
(Notes 8, 9)
MIN TYP MAX UNITS
– 57
V
– 1.5
– 9.5
V
– 12.5
– 21
V
– 37.7 –39.2 – 40.2
V
– 29.3 –30.5 – 31.5
V
3
mA
0.35 0.50 0.65
mA
±3.5
%
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Part Number LTC4257IS8
Description IEEE 802.3af PD Power over Ethernet Interface Controller
Maker Linear
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LTC4257IS8 Datasheet PDF






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