LTC4257IS8-1 Linear Technology, LTC4257IS8-1 Datasheet

IC CONTROLLER POE INTERFAC 8SOIC

LTC4257IS8-1

Manufacturer Part Number
LTC4257IS8-1
Description
IC CONTROLLER POE INTERFAC 8SOIC
Manufacturer
Linear Technology
Type
Power over Ethernet Switch (PoE)r
Datasheet

Specifications of LTC4257IS8-1

Applications
IP Phones, Power over LAN, Network Routers and Switches
Internal Switch(s)
Yes
Current Limit
350mA
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
8-SOIC (0.154", 3.90mm Width)
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LTC4257IS8-1
Manufacturer:
LT
Quantity:
10 000
Part Number:
LTC4257IS8-1
Manufacturer:
LT
Quantity:
8 917
Part Number:
LTC4257IS8-1#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Part Number:
LTC4257IS8-1#TRPBF
Manufacturer:
LINEAR
Quantity:
7 556
FEATURES
TYPICAL APPLICATIO
APPLICATIO S
Complete Power Interface Port for IEEE 802
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 × 3mm)
DFN Packages
IP Phone Power Management
Wireless Access Points
Telecom Power Control
POWER SOURCING
–48V FROM
EQUIPMENT
(PSE)
U
~
~
DF01SA
+
U
0.1µF
SMAJ58A
R
Controller with Dual Current Limit
CLASS
®
.3af
Powered Device (PD)
Power over Ethernet Interface
R
V
CLASS
IN
LTC4257-1
SIGDISA
PWRGD
DESCRIPTIO
The LTC
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 over-
load protection, signature disable and power good signal-
ling, 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 compat-
ibility 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 Lin-
ear 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 × 3mm) DFN packages.
All other trademarks are the property of their respective owners.
V
GND
OUT
, LTC and LT are registered trademarks of Linear Technology Corporation.
®
MIN
100k
5µF
4257-1 provides complete signature and power
+
SHDN
POWER SUPPLY
U
SWITCHING
RTN
V
IN
IEEE 802.3af PD
42571 TA01
TO LOGIC
3.3V
+
LTC4257-1
42571fb
1

Related parts for LTC4257IS8-1

LTC4257IS8-1 Summary of contents

Page 1

... Power Sourcing Equipment (PSE) applications. The LTC4257-1 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. Powered Device (PD) LTC4257-1 5µ ...

Page 2

... JA ORDER PART NUMBER LTC4257CS8-1 LTC4257IS8-1 Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grades are identified by a label on the shipping container. ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T SYMBOL PARAMETER V Signature Disable IH High Level Input Voltage V Signature Disable IL Low Level Input Voltage R Signature Disable INPUT Input Resistance V Power Good Output Low Voltage PG_OUT ...

Page 4

LTC4257 TYPICAL PERFOR A CE CHARACTERISTICS Input Current vs Input Voltage 25k Detection Range 0 25°C A 0.4 0.3 0.2 0 –4 –6 –8 –10 –2 INPUT VOLTAGE (V) 4357 G01 Input Current vs ...

Page 5

CTIO S NC (Pin 1): No Internal Connection. R (Pin 2): Class Select Input. Used to set the current CLASS value the LTC4257-1 maintains during classification. Con- nect a resistor between R and V CLASS ...

Page 6

LTC4257 APPLICATIO S I FOR ATIO The LTC4257-1 is intended for use as the front end of a Powered Device (PD) adhering to the IEEE 802.3af standard. The LTC4257-1 includes a trimmed 25k signature resistor, classification current source, ...

Page 7

U U APPLICATIO S I FOR ATIO summarized in Table 1. These various modes satisfy the requirements defined in the IEEE 802.3af specification. The input voltage is applied to the V reference to the GND pin. This input voltage is ...

Page 8

LTC4257 APPLICATIO S I FOR ATIO The power applied allowed to use either of two polarities and the PD must be able to accept this power common to install a diode ...

Page 9

U U APPLICATIO S I FOR ATIO specification. The LTC4257-1 is compatible with the IEEE 802.3af standard and also works with the obsolete Mea- sured Voltage method. In the Measured Current method (Figure 4), the PSE presents a fixed voltage ...

Page 10

LTC4257 APPLICATIO S I FOR ATIO Undervoltage Lockout The IEEE specification dictates a maximum turn-on volt- age of 42V and a minimum turn-off voltage of 30V for the PD. In addition, the PD must maintain large on-off hyster- ...

Page 11

U U APPLICATIO S I FOR ATIO accomplished by a dual level current limit. At turn on before C1 is charged, the LTC4257-1 current limit is set to the low level. After C1 is charged up and the V voltage ...

Page 12

LTC4257 APPLICATIO S I FOR ATIO If a sudden increase in voltage appears on the input line, this voltage step will be transferred through capacitor C1 and appear across the power MOSFET. The response of the LTC4257-1 will ...

Page 13

U U APPLICATIO S I FOR ATIO the overtemperature trip point. When the die cools down below the trip point, classification current is enabled again. If the PD is designed to operate at a high ambient tempera- ture and with ...

Page 14

LTC4257 APPLICATIO S I FOR ATIO The IEEE standard includes an AC impedance requirement in order to implement the AC disconnect function. Capaci- tor C14 in Figure 8 is used to meet this AC impedance requirement. A 0.1µF ...

Page 15

U U APPLICATIO S I FOR ATIO RJ45 + – – SPARE – SPARE 8 ISOLATED WALL TRANSFORMER OPTION 2: AUXILARY POWER INSERTED AFTER LTC4257-1 WITH ...

Page 16

LTC4257 APPLICATIO S I FOR ATIO that the transformer maintain the voltage between 38V and 57V to keep the LTC4257-1 in its normal operating range. The third option has the advantage of automatically dis- abling the 25k signature ...

Page 17

U U APPLICATIO S I FOR ATIO Signature Disable Interface To disable the 25k signature, connect the SIGDISA pin to the GND pin. Alternately, SIGDISA can be driven high with respect example of a signature disable ...

Page 18

LTC4257 APPLICATIO S I FOR ATIO 42571fb ...

Page 19

... RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ...

Page 20

... Quad IEEE 802.3af Power over Ethernet Controller LTC4259A-1 Quad IEEE 802.3af Power over Ethernet Controller LTC4267 IEEE 802.3af PD Interface Controller with Integrated Switching Regulator Burst Mode is a registered trademark of Linear Technology Corporation Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● ...

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