ltc4267-3 Linear Technology Corporation, ltc4267-3 Datasheet - Page 8

• Manufacturer Part Number: ltc4267-3
• Description: Power Over Ethernet Ieee 802.3af Pd Interface With Integrated 300khz Switching Regulator
• Manufacturer: Linear Technology Corporation

PI FU CTIO S
LTC4267-3
8
PGND (Pins 2, 15/Pins 1, 8, 9, 16): Switching Regulator
Negative Supply. This pin is the negative supply rail for the
switching regulator controller and must be tied to P
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.
NGATE (Pin 3): Gate Driver Output. This pin drives the
regulator’s external N-Channel MOSFET and swings from
PGND to P
P
pin is the positive supply rail for the switching regulator
and must be closely decoupled to PGND.
R
value the PD maintains during classifi cation. Connect a
resistor between R
NC (Pins 6, 8, 9/Pin 6): No Internal Connection.
V
input port through the input diodes.
P
ing regulator PGND pin and any additional PD loads through
an internal power MOSFET that limits input current. P
is high impedance until the voltage reaches the turn-on
UVLO threshold. The output is then current limited. See
the Application Information section.
TH
VCC
PORTN
OUT
CLASS
U
/RUN (Pin 1/Pin 2): Current Threshold/Run Input. This
(Pin 10): Power Output. Supplies –48V to the switch-
(Pin 4): Switching Regulator Positive Supply. This
(Pin 5): Class Select Input. Used to set the current
(Pin 7): Negative Power Input. Tie to the –48V
U
VCC
.
CLASS
U
and V
(DFN/SSOP)
PORTN
(see Table 2).
OUT
OUT
.
PWRGD (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. PWRGD is high impedance during detec-
tion, classifi cation and in the event of a thermal overload.
PWRGD is referenced to V
SIGDISA (Pin 12): Signature Disable Input. SIGDISA al-
lows 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 LTC4267-3. If unused, tie SIGDISA to
V
V
port power return through the input diodes.
SENSE (Pin 14): Current Sense. This pin performs two
functions. It monitors the regulator switch current by read-
ing 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.
Exposed Pad (Pin 17, DFN Only): Ground. The Exposed
Pad must be soldered to an electrically isolated PCB heat
sink.
PORTN
PORTP
FB
(Pin 16/Pin 15): Feedback Input. Receives the feed-
.
(Pin 13): Positive Power Input. Tie to the input
PORTN
.
PORTP
lowers
42673f