Datasheet

LTC4290/LTC4271
17
429071fa
For more information www.linear.com/LTC4290
Extended Power LTPoE
++
A-grade LTC4290/LTC4271 parts add the capability to
autonomously deliver up to 90W of power to the PD.
LTPoE
++
PDs may forgoe 802.3 LLDP support and rely
solely on the LTPoE
++
Physical Classification to negotiate
power with LTPoE
++
PSEs; this greatly simplifies high-
power PD
implementations.
LTPoE
++
may be optionally enabled for A-grade LTC4290/
LTC4271s by setting both the High Power Enable and
LTPoE
++
Enable bits.
The higher levels of LTPoE
++
delivery impose additional
layout and component selection constraints. LTC4290 pin
selects allow the AUTO pin mode LTC4271 to autonomously
power up to supported power levels. If the AUTO pin is
high, the XIO1 and XIO0 pins are sampled at reset to de
-
termine the maximum deliverable power. PDs requesting
more than the available power limits are not powered.
Table 1. LTPoE
++
AUTO Pin Mode Maximum Delivered Power
Capabilities
POWER XIO1 XIO0
38.7W 0 0
52.7W 0 1
70W 1 0
90W 1 1
BACKWARD COMPATIBILITY
The LTC4290/LTC4271 chipset is designed to be backward
compatible with the LTC4266, operating in Type 2 mode,
without software changes; only minor layout changes
are required to implement a fully compliant IEEE 802.3at
design.
Some LTC4266 registers have been obsoleted in the
LTC4290/LTC4271 chipset. The obsoleted registers are not
required for 802.3at compliant PSE operation. For more
details about software differences between the LTC4266
and LTC4290/LTC4271, refer to the LTC4271 Software
Programming document.
Operation with high power mode disabled is obsoleted in
the LTC4290/LTC4271 chipset. All operations previously
available in low power mode are fully implemented as a
subset of the high power mode capabilities.
ApplicAtions inForMAtion
OPERATING MODES
The LTC4290/LTC4271 includes eight independent ports,
each of which can operate in one of four modes: manual,
semi-auto, AUTO pin, or shutdown.
Table 2. Operating Modes
MODE AUTO
PIN
OPMD DETECT/
CLASS
POWER-UP AUTOMATIC
I
CUT
/I
LIM
ASSIGNMENT
AUTO Pin 1 11b Enabled
at Reset
Automatically Yes
Reserved 0 11b N/A N/A N/A
Semi-auto 0 10b Host
Enabled
Upon
Request
No
Manual 0 01b Once
Upon
Request
Upon
Request
No
Shutdown 0 00b Disabled Disabled No
In manual mode, the port waits for instructions from the
host system before taking any action. It runs a single
detection or classification cycle when commanded to by
the host, and reports the result in its Port Status register.
The host system can command the port to turn on or off
the power at any time.
In semi-auto mode, the port repeatedly attempts to detect
and classify any PD attached to it. It reports the status of
these attempts back to the host, and waits for a command
from the host before turning on power to the port. The
host must enable detection (and optionally classification)
for the port before detection will start.
AUTO pin mode operates the same as semi-auto mode
except it will automatically turn on the power to the port if
detection is successful. AUTO pin mode will autonomously
set the I
CUT
and I
LIM
values based on the class result. This
operational mode is only valid if the AUTO pin is high at
reset or power-up and remains high during operation.
In shutdown mode, the port is disabled and will not detect
or power a PD.
Regardless of which mode it is in, the LTC4290/LTC4271
will remove power automatically from any port that gener
-
ates a current limit fault. It will also automatically remove
power from any port that generates a disconnect event if
disconnect detection
is enabled. The host controller may
also command the port to remove power at any time.