Datasheet

LTC4257-1
5
42571fb
NC (Pin 1): No Internal Connection.
R
CLASS
(Pin 2): Class Select Input. Used to set the current
value the LTC4257-1 maintains during classification. Con-
nect a resistor between R
CLASS
and V
IN
(see Table 2).
NC (Pin 3): No Internal Connection.
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. The output is then
current limited. See Applications Information.
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
IN
.
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
IN
. If unused, tie SIGDISA
to V
IN
.
GND (Pin 8): Ground. Tied to system ground and power
return through the input diode bridge.
UU
U
PI FU CTIO S
BLOCK DIAGRA
W
42571 BD
V
IN
BOLD LINE INDICATES HIGH CURRENT PATH
V
OUT
–
+
8
54
NC
3
R
CLASS
2
NC
PWRGD
SIGDISA
GND
1
7
6
CONTROL
CIRCUITS
INPUT
CURRENT
LIMIT
POWER GOOD
CLASSIFICATION
CURRENT LOAD
1.237V
EN
375mA
140mA
SIGNATURE DISABLE
9k
16k
0.3Ω
–
+
EN
25k SIGNATURE
RESISTOR