LTC4269CDKD-1#TRPBF Linear Technology, LTC4269CDKD-1#TRPBF Datasheet - Page 14

• Manufacturer Part Number: LTC4269CDKD-1#TRPBF
• Description: IC PD/OPTO FLYBACK CTRLR 32-DFN
• Manufacturer: Linear Technology
• Type: Power Over Ethernet (PoE)r

Specifications of LTC4269CDKD-1#TRPBF

• Applications: Power Interface Switch for Power Over Ethernet (PoE) Devices
• Voltage - Supply: 14 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 32-DFN
• Current - Supply: 1.35mA
• Interface: IEEE 802.3af
• Controller Type: Powered Device Interface Controller (PD)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
LTC4269-1
SIGNATURE CORRUPT OPTION
In some designs that include an auxiliary power option,
it is necessary to prevent a PD from being detected by a
PSE. The LTC4269-1 signature resistance can be corrupted
with the SHDN pin (Figure 3). Taking the SHDN pin high
will reduce the signature resistor below 11k which is an
invalid signature per the IEEE 802.3af/IEEE 802.3at speci-
fi cation, and alerts the PSE not to apply power. Invoking
the SHDN pin also ceases operation for classifi cation and
disconnects the LTC4269-1 load from the PD input. 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 do not support classifi cation. Class 1-3 partitions
PDs into three distinct power ranges. Class 4 includes the
new power range under IEEE802.3at (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 LTC4269-1 asserts a load current representing the
PD power classifi cation. The classifi cation load current
is programmed with a resistor R
from Table 2.
14
PSE
TO
Figure 3. 25k Signature Resistor with Disable
SHDN
LTC4269-1
V
PORTN
16k
SIGNATURE DISABLE
CLASS
25k SIGNATURE
RESISTOR
PORTN
V
that is chosen
PORTP
.
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Table 2. Summary of Power Classifi cations and LTC4269-1
R
CLASS
0
1
2
3
4
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
communicating over the high speed data line (layer 2). A
Type 2 PD must recognize both layers of communication.
Since layer 2 communication takes place directly between
the PSE and the LTC4269-1 load, the LTC4269-1 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
when the PSE presents an input voltage between 15.5V
to 20.5V and the LTC4269-1 presents a class 4 load cur-
rent. The PSE then drops the input voltage into the mark
voltage range of 7V 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
LTC4269-1 that a Type 2 PSE is present. The Type 2 PSE
then applies power to the PD and the LTC4269-1 charges
up the reservoir capacitor C1 with a controlled inrush cur-
rent. When C1 is fully charged, and the LTC4269-1 declares
power good, the T2P pin presents an active low signal, or
low impedance output with respect to V
output becomes inactive when the LTC4269-1 input voltage
falls below undervoltage lockout threshold.
CLASS
Resistor Selection
USAGE
Type 1
Type 1
Type 1
Type 1
Type 2
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)
CLASSIFICATION
LOAD CURRENT
NOMINAL
(mA)
< 0.4
10.5
18.5
28
40
PORTN
. The T2P
LTC4269-1
RESISTOR
(Ω, 1%)
R
Open
69.8
45.3
30.9
CLASS
124
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