LTC4270/LTC4271
APPLICATIONS INFORMATION
Extended Power LTPoE
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OPERATING MODES
A-grade LTC4270/LTC4271 parts add the capability to
autonomously deliver up to 90W of power to the PD.
The LTC4270/LTC4271 includes 12 independent ports,
each of which can operate in one of four modes: manual,
semi-auto, AUTO pin, or shutdown.
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LTPoE PDs may forgoe 802.3 LLDP support and rely
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solely on the LTPoE Physical Classification to negotiate
Table 2. Operating Modes
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power with LTPoE PSEs; this greatly simplifies high-
MODE
AUTO OPMD DETECT/ POWER-UP
AUTOMATIC
/I
power PD implementations.
PIN
CLASS
I
CUT LIM
ASSIGNMENT
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LTPoE may be optionally enabled for A-grade LTC4270/
AUTO Pin
1
11b
Enabled Automatically
at Reset
Yes
LTC4271s by setting both the High Power Enable and
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LTPoE Enable bits.
Reserved
Semi-auto
0
0
11b
10b
N/A
N/A
N/A
No
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The higher levels of LTPoE delivery impose additional
layout and component selection constraints. LTC4270 pin
selectsallowtheAUTOpinmodeLTC4271toautonomously
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.
Host
Enabled
Upon
Request
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.
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Table 1. LTPoE AUTO Pin Mode Maximum Delivered Power
Capabilities
POWER
35W
XIO1
XIO0
0
0
1
1
0
1
0
1
45W
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.
70W
90W
BACKWARDS COMPATIBILITY
TheLTC4270/LTC4271chipsetisdesignedtobebackward
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.
AUTO pin mode operates the same as semi-auto mode
except it will automatically turn on the power to the port if
detectionissuccessful.AUTOpinmodewillautonomously
and I values based on the class result. This
operational mode is only valid if the AUTO pin is high.
set the I
CUT
LIM
Some LTC4266 registers have been obsoleted in the
LTC4270/LTC4271chipset.Theobsoletedregistersarenot
required for 802.3at compliant PSE operation. For more
details about software differences between the LTC4266
and LTC4270/LTC4271, refer to the LTC4271 Software
Programming document.
In shutdown mode, the port is disabled and will not detect
or power a PD.
Regardless of which mode it is in, the LTC4270/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.
Operation with high power mode disabled is obsoleted in
the LTC4270/LTC4271 chipset. All operations previously
available in low power mode are fully implemented as a
subset of the high power mode capabilities.
42701f
18
Linear [ Linear ]
