ltc4269cdkd-2 Linear Technology Corporation, ltc4269cdkd-2 Datasheet - Page 15

• Manufacturer Part Number: ltc4269cdkd-2
• Description: Ieee 802.3at High Power Pd And Synchronous Forward Controller With Aux Support
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
also ceases operation for classifi cation and turns off the
internal Hot Swap FET. If this feature is not used, connect
SHDN to V
CLASSIFICATION
Classifi cation provides a method for more effi cient power
allocation by allowing the PSE to identify a PD power clas-
sifi cation. Class 0 is included in the IEEE specifi cation for
PDs that don’t support classifi cation. Class 1-3 partitions
PDs into three distinct power ranges. Class 4 includes the
new power range under IEEE 802.3at (see Table 2).
During classifi cation probing, the PSE presents a fi xed
voltage between 15.5V and 20.5V to the PD (Figure 1).
The LTC4269-2 asserts a load current representing the
PD power classifi cation. The classifi cation load current
is programmed with a resistor R
from Table 2.
Table 2. Summary of Power Classifi cations and LTC4269-2
R
2-EVENT CLASSIFICATION AND THE T2P PIN
A Type 2 PSE may declare the availability of high power by
performing a 2-event classifi cation (Layer 1) or by com-
municating over the high speed data line (Layer 2). A Type
2 PD must recognize both layers of communication. Since
CLASS
CLASS
0
1
2
3
4
PSE
TO
Resistor Selection
USAGE
Figure 3. 25k Signature Resistor with Disable
Type 1
Type 1
Type 1
Type 1
Type 2
PORTN
SHDN
V
LTC4269-2
PORTN
POWER LEVELS
AT INPUT OF PD
.
0.44 to 12.95
6.49 to 12.95
12.95 to 25.5
0.44 to 3.84
3.84 to 6.49
MAXIMUM
(W)
14k
CLASSIFICATION
LOAD CURRENT
SIGNATURE DISABLE
NOMINAL
25k SIGNATURE
RESISTOR
(mA)
CLASS
<0.4
10.5
18.5
28
40
V
PORTP
that is chosen
42692 F03
LTC4269-2
RESISTOR
(Ω, 1%)
R
Open
69.8
45.3
30.9
CLASS
124
Layer 2 communications takes place directly between the
PSE and the PD, the LTC4269-2 concerns itself only with
recognizing 2-event classifi cation.
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
DETECTION V1
PSE
DETECTION I
DETECTION V2
DETECTION I
Figure 4. V
Result of 2-Event Classifi cation
40mA
INRUSH = 100mA R
I
LOAD
–10
–20
–30
–40
–50
R
50
40
30
20
10
50
40
30
20
10
CLASS
I
IN
=
1
1ST CLASS
2
V
R
1ST CLASS
PORTP
LOAD
NEG
2ND CLASS
2ND CLASS
R
V
dV
dt
CLASS
PORTN
INRUSH
, T2P and PD Current as a
UVLO
LTC4269-2
=
CLASS
INRUSH
1ST MARK
2ND MARK
2ND MARK
1ST MARK
C1
V
PORTP
V
= 30.9Ω
T2P
NEG
ON
ON
LTC4269-2
UVLO
= R
TRACKS
V
UVLO
R
PORTN
LOAD, I
LOAD
42692 F04
LOAD
TIME
TIME
TIME
C1
C1
LOAD
15
42692f