LTC4265 LINER [Linear Technology], LTC4265 Datasheet - Page 9

• Manufacturer Part Number: LTC4265
• Description: IEEE 802.3at High Power PD Interface Controller with 2-Event Classifi cation Recognition
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
In 2-event classifi cation, a Type-2 PSE probes for power
classifi cation twice. Figure 4 presents an example of a
2-event classifi cation. The 1st classifi cation event occurs
when the PSE presents an input voltage between 14.5V to
20.5V and the LTC4265 presents a class 4 load current.
The PSE then drops the input voltage into the mark volt-
age range of 6.9V to 10V, signaling the 1st mark event.
The PD in the mark voltage range presents a load current
between 0.25mA to 4mA.
The PSE repeats this sequence, signaling the 2nd Clas-
sifi cation and 2nd mark event occurrence. This alerts the
LTC4265 that a Type-2 PSE is present. The Type-2 PSE
then applies power to the PD and the LTC4265 charges
up the reservoir capacitor C1 with a controlled inrush cur-
rent. When C1 is fully charged, and the LTC4265 declares
power good, the T2PSE pin presents an active low signal,
or low impedance output with respect to V
output becomes inactive when the LTC4265 input voltage
falls outside the normal operating range.
SIGNATURE CORRUPT DURING MARK
As a member of the IEEE802.3at working group, Linear
notes that it is possible for a Type-2 PD to receive a
false indication of a 2-event classifi cation if a PSE port
is pre-charged to a voltage above the detection voltage
range before the fi rst detection cycle. The IEEE working
group modifi ed the standard to prevent this possibility by
requiring a Type-2 PD to corrupt the signature resistance
during the mark event, alerting the PSE not to apply power.
The LTC4265 conforms to this standard by internally
corrupting the signature resistance. This also discharges
the port before the PSE begins the next detection cycle.
IN
. The T2PSE
PSE
DETECTION V1
DETECTION V1
DETECTION V2
DETECTION V2
Figure 4. V
as a Result of 2-event Classifi cation
40mA
R
INRUSH = 100mA
I
LOAD
–10
–20
–30
–40
–50
CLASS
I
50
40
30
20
10
50
40
30
20
10
IN
=
R
1st CLASS
1st CLASS
V
LOAD
IN
dV
1st MARK 2nd MARK
1st MARK 2nd MARK
dt
OUT
R
V
2nd CLASS
2nd CLASS
=
IN
CLASS
LTC4265
INRUSH
, T2PSE, and PD Current
INRUSH
UVLO
C1
T2PSE
V
GND
OUT
R
CLASS
ON
ON
= 30.9Ω
R
UVLO
= R
TRACKS
LTC4265
UVLO
LOAD
C1
LOAD, I
V
LOAD
IN
TIME
TIME
TIME
4265 F04
C1
V
LOAD
OUT
GND
9
4265f