ltc4257cs8-trpbf Linear Technology Corporation, ltc4257cs8-trpbf Datasheet - Page 5

• Manufacturer Part Number: ltc4257cs8-trpbf
• Description: Ieee 802.3af Pd Power Over Ethernet Interface Controller
• Manufacturer: Linear Technology Corporation

PI FU CTIO S
BLOCK DIAGRA
NC (Pin 1): No Connect.
R
current the LTC4257 maintains during classification. Con-
nect a resistor between R
NC (Pin 3): No Connect.
V
input diode bridge.
V
through an internal power MOSFET that limits input cur-
rent. V
above the turn-on UVLO threshold. Above the UVLO
threshold the output is current limited to 350mA.
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): External Class Select Input. Used to set the
U
is high impedance until the input voltage rises
R
CLASS
U
V
NC
NC 3
IN
1
2
4
CLASS
W
CONTROL
CIRCUITS
0.3Ω
and V
1.237V
350mA
IN
(see Table 2).
–
+
+
–
CURRENT SOURCE
CLASSIFICATION
EN
EN
CURRENT
INPUT
LIMIT
BOLD LINE INDICATES HIGH CURRENT PATH
PWRGD (Pin 6): Power Good Output, Open-Drain. Signals
that the LTC4257 MOSFET is fully on. Low impedance
indicates power is good. PWRGD is high impedance
during detection, classification and in the event of a
thermal overload. PWRGD is referenced to V
NC (Pin 7): No Connect
GND (Pin 8): Ground. Tie to system ground and to power
return through the input diode bridge.
POWER GOOD
25k SIGNATURE
RESISTOR
8
7
6
5
4257 BD
V
GND
NC
PWRGD
OUT
LTC4257
IN
.
4257fb
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