LTC4267 LINER [Linear Technology], LTC4267 Datasheet - Page 8

• Manufacturer Part Number: LTC4267
• Description: Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator
• Manufacturer: LINER [Linear Technology]

PI FU CTIO S
LTC4267
I
pin performs two functions. It serves as the switching
regulator error amplifi er compensation point as well as
the run/shutdown control input. Nominal voltage range is
0.7V to 1.9V. Forcing the pin below 0.28V with respect to
PGND causes the controller to shut down.
PGND (Pin 1, 8, 9, 16/Pin 2, 15): Switching Regulator
Negative Supply. This pin is the negative supply rail for the
switching regulator controller and must be tied to P
NGATE (Pin 3/Pin 3): Gate Driver Output. This pin drives
the regulator’s external N-Channel MOSFET and swings
from PGND to P
P
This pin is the positive supply rail for the switching regula-
tor and must be closely decoupled to PGND.
R
rent value the PD maintains during classifi cation. Connect
a resistor between R
V
–48V input port through the input diodes.
P
the switching regulator PGND pin and any additional PD
loads through an internal power MOSFET that limits input
current. P
the turn-on UVLO threshold. The output is then current
limited. See the Application Information section.
8
TH
VCC
CLASS
PORTN
OUT
U
/RUN (Pin 2/Pin 1): Current Threshold/Run Input. This
(Pin 4/Pin 4): Switching Regulator Positive Supply.
(Pin 10/Pin 10): Power Output. Supplies –48V to
(Pin 5/Pin 5): Class Select Input. Used to set the cur-
(Pin 7/Pin 7): Negative Power Input. Tie to the
OUT
U
is high impedance until the voltage reaches
VCC
.
U
CLASS
(GN/DHC)
and V
PORTN
(see Table 2).
OUT
.
⎯ P ⎯ W ⎯ R ⎯ G ⎯ D (Pin 11/Pin 11): Power Good Output, Open-Drain.
Indicates that the PD MOSFET is on and the switching
regulator can start operation. Low impedance indicates
power is good. ⎯ P ⎯ W ⎯ R ⎯ G ⎯ D is high impedance during detec-
tion, classifi cation and in the event of a thermal overload.
⎯ P ⎯ W ⎯ R ⎯ G ⎯ D is referenced to V
SIGDISA (Pin 12/Pin 12): Signature Disable Input. SIGDISA
allows the PD to present an invalid signature resistance
and remain inactive. Connecting SIGDISA to V
the signature resistance to an invalid value and disables
all functions of the LTC4267. If unused, tie SIGDISA to
V
V
input port power return through the input diodes.
SENSE (Pin 14/Pin 14): Current Sense. This pin performs
two functions. It monitors the regulator switch current by
reading the voltage across an external sense resistor. It also
injects a current ramp that develops a slope compensation
voltage across an optional external programming resistor.
See the Applications Information section.
V
back voltage from the external resistor divider across the
output.
NC (Pin 6/Pin 6, 8, 9): No Internal Connection.
Backside Connection (DHC Only, Pin 17): Exposed Pad.
This exposed pad must be soldered to an electrically isolated
and thermally conductive PC board heat sink.
PORTN
PORTP
FB
(Pin 15/Pin 16): Feedback Input. Receives the feed-
.
(Pin 13/Pin 13): Positive Power Input. Tie to the
PORTN
.
PORTP
lowers
4267f