Datasheet

LTC4257
5
4257fb
NC (Pin 1): No Connect.
R
CLASS
(Pin 2): External Class Select Input. Used to set the
current the LTC4257 maintains during classification. Con-
nect a resistor between R
CLASS
and V
IN
(see Table 2).
NC (Pin 3): No Connect.
V
IN
(Pin 4): Power Input. Tie to system –48V through the
input diode bridge.
V
OUT
(Pin 5): Power Output. Supplies –48V to the PD load
through an internal power MOSFET that limits input cur-
rent. V
OUT
is high impedance until the input voltage rises
above the turn-on UVLO threshold. Above the UVLO
threshold the output is current limited to 350mA.
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
IN
.
NC (Pin 7): No Connect
GND (Pin 8): Ground. Tie to system ground and to power
return through the input diode bridge.
UU
U
PI FU CTIO S
BLOCK DIAGRA
W
4257 BD
V
IN
BOLD LINE INDICATES HIGH CURRENT PATH
V
OUT
–
+
8
54
NC
3
R
CLASS
2
NC
PWRGD
GND
7
NC
1
6
CONTROL
CIRCUITS
INPUT
CURRENT
LIMIT
350mA
POWER GOOD
CLASSIFICATION
CURRENT SOURCE
1.237V
EN
0.3Ω
–
+
EN
25k SIGNATURE
RESISTOR