LTC4266 LINER [Linear Technology], LTC4266 Datasheet - Page 16

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LTC4266

Manufacturer Part Number
LTC4266
Description
Quad IEEE 802.3at Power over Ethernet Controller
Manufacturer
LINER [Linear Technology]
Datasheet

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LTC4266
Operating Modes
The LTC4266 includes four independent ports, each of
which can operate in one of four modes: manual, semi-
auto, AUTO pin or shutdown.
Table 1. Operating Modes
MODE
AUTO Pin
Reserved
Semi-auto
Manual
Shutdown
• In manual mode, the port waits for instructions from the
• In semi-auto mode, the port repeatedly attempts to
• AUTO pin mode operates the same as semi-auto mode
• In shutdown mode, the port is disabled and will not
Regardless of which mode it is in, the LTC4266 will remove
power automatically from any port that generates 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 com-
mand the port to remove power at any time.
APPLICATIONS INFORMATION
16
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. This mode should only
be used for diagnostic and test purposes.
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.
except that it will automatically turn on the power to the
port if detection is successful. In AUTO pin mode, I
and I
AUTO pin must be high at reset to ensure proper AUTO
pin mode operation.
detect or power a PD.
LIM
AUTO
values are set automatically by the LTC4266. The
PIN
0
0
1
0
0
OPMD
11b
11b
10b
01b
00b
Once Upon
Enabled at
DETECT/
Disabled
Request
Enabled
CLASS
Reset
Host
N/A
Automatically
POWER-UP
Disabled
Request
Request
Upon
Upon
N/A
ASSIGNMENT
AUTOMATIC
I
CUT
Yes
N/A
No
No
No
/I
LIM
CUT
Reset and the AUTO/MID Pins
The initial LTC4266 configuration depends on the state
of the AUTO and MID pins during reset. Reset occurs at
power-up, or whenever the RESET pin is pulled low or the
global Reset All bit is set. Note that the AUTO pin is only
sampled when a reset occurs. Changing the state of AUTO
or MID after power-up will not change the port behavior
of the LTC4266 until a reset occurs.
Although typically used with a host controller, the LTC4266
can also be used in a standalone mode with no connection
to the serial interface. If there is no host present, the AUTO
pin should be tied high so that, at reset, all ports will be
configured to operate automatically. Each port will detect
and classify repeatedly until a PD is discovered, set I
and I
after successful detection, and remove power when a PD
is disconnected. Similarly, if the standalone application
is a midspan, the MID pin should be tied high to enable
correct midspan detection timing.
Table 2 shows the I
cally set in AUTO pin mode, based on the discovered class.
Table 2. I
CLASS
Class 1
Class 2
Class 3 or Class 0
Class 4
The automatic setting of the I
curs if the LTC4266 is reset with the AUTO pin high.
DETECTION
Detection Overview
To avoid damaging network devices that were not designed
to tolerate DC voltage, a PSE must determine whether the
connected device is a real PD before applying power. The
IEEE specification requires that a valid PD have a common
mode resistance of 25k ±5% at any port voltage below 10V.
The PSE must accept resistances that fall between 19k and
26.5k, and it must reject resistances above 33kΩ or below
15k (shaded regions in Figure 11). The PSE may choose to
LIM
according to the classification results, apply power
CUT
and I
LIM
CUT
Values in AUTO pin mode
and I
112mA
206mA
375mA
638mA
LIM
I
CUT
CUT
values that will be automati-
and I
LIM
values only oc-
425mA
425mA
425mA
850mA
I
LIM
4266fb
CUT

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