LTC4257IS8-1 Linear Technology, LTC4257IS8-1 Datasheet - Page 5

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

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

BLOCK DIAGRA
PI FU CTIO S
NC (Pin 1): No Internal Connection.
R
value the LTC4257-1 maintains during classification. Con-
nect a resistor between R
NC (Pin 3): No Internal Connection.
V
input diode bridge.
V
through an internal power MOSFET that limits input cur-
rent. V
above the turn-on UVLO threshold. The output is then
current limited. See Applications Information.
IN
OUT
CLASS
U
(Pin 4): Power Input. Tie to system – 48V through the
(Pin 5): Power Output. Supplies – 48V to the PD load
OUT
(Pin 2): Class Select Input. Used to set the current
U
is high impedance until the input voltage rises
R
CLASS
U
V
NC
NC 3
IN
1
2
4
CLASS
W
375mA
140mA
CONTROL
CIRCUITS
and V
0.3Ω
1.237V
CLASSIFICATION
CURRENT LOAD
IN
(see Table 2).
+
–
+
–
EN
EN
INPUT
CURRENT
LIMIT
25k SIGNATURE
BOLD LINE INDICATES HIGH CURRENT PATH
PWRGD (Pin 6): Power Good Output, Open-Drain. Signals
to the PD load that the LTC4257-1 MOSFET is on and that
the PD’s DC/DC converter can start operation. Low imped-
ance indicates power is good. PWRGD is high impedance
during detection, classification and in the event of a
thermal overload. PWRGD is referenced to V
SIGDISA (Pin 7): Signature Disable Input. Allows the PD
to command the LTC4257-1 to present an invalid signa-
ture resistance and to remain inactive. Connecting SIGDISA
to GND lowers the signature resistance to an invalid value
and disables all functions of the LTC4257-1. If left floating,
SIGDISA is internally pulled to V
to V
GND (Pin 8): Ground. Tied to system ground and power
return through the input diode bridge.
RESISTOR
POWER GOOD
IN
.
9k
16k
SIGNATURE DISABLE
8
7
6
5
IN
42571 BD
V
. If unused, tie SIGDISA
GND
SIGDISA
PWRGD
OUT
LTC4257-1
IN
.
42571fb
5