LTC4258 LINER [Linear Technology], LTC4258 Datasheet - Page 8

• Manufacturer Part Number: LTC4258
• Description: Quad IEEE 802.3af Power over Ethernet Controller with Integrated Detection
• Manufacturer: LINER [Linear Technology]

LTC4258
PI FU CTIO S
AGND (Pin 21): Analog Ground. AGND should be con-
nected to the return from the – 48V supply. AGND and
DGND should be tied together.
SENSE4 (Pin 22): Port 4 Current Sense Input. SENSE4
monitors the external MOSFET current via a 0.5 sense
resistor between SENSE4 and V
across the sense resistor exceeds the overcurrent detec-
tion threshold V
If the voltage across the sense resistor reaches the current
limit threshold V
GATE4 pin voltage is lowered to maintain constant current
in the external MOSFET. See Applications Information for
further details. If the port is unused, the SENSE4 pin must
be tied to V
GATE4 (Pin 23): Port 4 Gate Drive. GATE4 should be
connected to the gate of the external MOSFET for port 4.
When the MOSFET is turned on, a 50 A pull-up current
source is connected to the pin. The gate voltage is clamped
to 13V (typ) above V
the voltage at GATE4 will be reduced to maintain constant
current through the external MOSFET. If the fault timer
expires, GATE4 is pulled down with 50 A, turning the
MOSFET off and recording a t
port is unused, float the GATE4 pin or tie it to V
OUT4 (Pin 24): Port 4 Output Voltage Monitor. OUT4
should be connected to the output port through a 10k
series resistor. A current limit foldback circuit limits the
power dissipation in the external MOSFET by reducing the
current limit threshold when the port voltage is within 18V
of AGND. The port 4 Power Good bit is set when the voltage
8
U
U
EE
.
CUT
LIM
, the current limit fault timer counts up.
U
EE
(typically 25mV/50mA higher), the
. During a current limit condition,
ICUT
EE
. Whenever the voltage
or t
START
event. If the
EE
.
from OUT4 to V
is connected internally from OUT4 to AGND. If the port is
unused, the OUT4 pin can be tied to AGND or allowed to
float.
SENSE3 (Pin 25): Port 3 Current Sense Input. See SENSE4.
GATE3 (Pin 26): Port 3 Gate Drive. See GATE4.
OUT3 (Pin 27): Port 3 Output Voltage Monitor. See OUT4.
V
– 57V supply, relative to AGND.
SENSE2 (Pin 29): Port 2 Current Sense Input. See SENSE4.
GATE2 (Pin 30): Port 2 Gate Drive. See GATE4.
OUT2 (Pin 31): Port 2 Output Voltage Monitor. See OUT4.
SENSE1 (Pin 32): Port 1 Current Sense Input. See SENSE4.
GATE1 (Pin 33): Port 1 Gate Drive. See GATE 4.
OUT1 (Pin 34): Port 1 Output Voltage Monitor. See OUT4.
AUTO (Pin 35): Auto Mode Input. Auto mode is intended
to allow the LTC4258 to detect and power up a PD even if
there is no host controller present on the I
voltage of the AUTO pin determines the state of the
internal registers when the LTC4258 is reset or comes out
of V
of these register bits can subsequently be changed via the
I
can be read at bit 0 in the Pin Status register (11h). Pull
AUTO high or low with 10k or tie to V
NC (Pin 36): No Internal Connection.
2
EE
C interface if desired. The real-time state of the AUTO pin
DD
(Pin 28): – 48V Supply Input. Connect to a – 48V to
UVLO (see the Register map in Table 1). The states
EE
drops below 2V (typ). A 2.5M resistor
DD
or DGND.
2
C bus. The
4258p