ltc4270 Linear Technology Corporation, ltc4270 Datasheet - Page 24

• Manufacturer Part Number: ltc4270
• Description: 12-port Poe/poe+/ltpoe++ Pse Controller
• Manufacturer: Linear Technology Corporation

LTC4270/LTC4271
APPLICATIONS INFORMATION
Port Current Policing
The LTC4270/LTC4271 can augment t
ing with a policing function to track the one second current
averages. A port violating the user-specified Port Police
Threshold will be shut off with both a t
recorded. A port current Police event can be differentiated
from a port t
bits are set for a Police violation while only the t
set for t
Port Voltage Readback
The LTC4270/LTC4271 measures the output voltage at each
port with an internal A/D converter. Port data is only valid
when the port power is on and reads zero at all other times.
Disconnect
The LTC4270/LTC4271 monitors powered ports to ensure
the PD continues to draw the minimum specified current. A
disconnect timer counts up whenever port current is below
7.5mA (typ), indicating that the PD has been disconnected.
If the t
disconnect bit in the fault event register will be set. If the
current returns before the t
resets. As long as the PD exceeds the minimum current
level more often than t
Although not recommended, the DC disconnect feature
can be disabled by clearing the corresponding enable bits.
Note that this defeats the protection mechanisms built
into the IEEE specification, since a powered port will stay
powered after the PD is removed. If the still-powered port
is subsequently connected to a non-PoE data device, the
device may be damaged.
The LTC4270/LTC4271 does not include AC disconnect
circuitry, but includes AC Disconnect Enable bits to main-
tain compatibility with the LTC4259A. If the AC Disconnect
Enable bits are set, DC disconnect will be used.
24
DIS
CUT
timer expires, the port will be turned off and the
timer violations.
CUT
violation by reading both events bits; both
DIS
, it will remain powered.
DIS
timer runs out, the timer
CUT
CUT
current monitor-
and Police event
CUT
bit is
Masked Shutdown
The LTC4270/LTC4271 provides a low latency port shed-
ding feature to quickly reduce the system load when
required. By allowing a pre-determined set of ports to
be turned off, the current on an overloaded main power
supply can be reduced rapidly while keeping high priority
devices powered. Each port can be configured to high or
low priority; all low-priority ports will shut down within
6.5μs after the MSD pin is pulled low, high priority ports
will remain powered. If a port is turned off via MSD, the
corresponding Detection and Classification Enable bits are
cleared, so the port will remain off until the host explicitly
re-enables detection.
In the LTC4270/LTC4271 chipset the active level of MSD
is register configurable as active high or low. The default
is LTC4266-compatible active low behavior.
Temperature and V
The LTC4270/LTC4271 measures the analog die tempera-
ture and V
General Purpose IO
Two sets of general purpose IO pins are available in the
LTC4270/LTC4271 chipset. The first set of general purpose
IO are GP1 and GP0. These fully bidirectional IO are 3.3V
CMOS IO on the LTC4271 chip.
The second set of general purpose IO pins are XIO1 and
XIO0. These fully bidirectional IO are 4.3V CMOS IO on
the LTC4270 chip.
Code Download
LTC4271 firmware is field-upgradable by downloading
and executing RAM images. RAM images are volatile
and must be re-downloaded after each V
but will remain valid during reset and V
Contact Linear Technology for code download procedures
and RAM images.
EE
voltage with an internal 12-bit A/D converter.
EE
Readback
EE
DD
power events.
power cycle,
42701f