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

IC PD/OPTO FLYBACK CTRLR 32-DFN

LTC4269CDKD-1#PBF

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

Specifications of LTC4269CDKD-1#PBF

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)
Input Voltage
60V
Supply Current
6.4mA
Digital Ic Case Style
DFN
No. Of Pins
32
Duty Cycle (%)
88%
Frequency
100kHz
Operating Temperature Range
0°C To +70°C
Msl
MSL 1 - Unlimited
Rohs Compliant
Yes
Operating Temperature (max)
70C
Operating Temperature (min)
0C
Pin Count
32
Mounting
Surface Mount
Package Type
DFN EP
Case Length
7mm
Screening Level
Commercial
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
LTC4269-1
APPLICATIONS INFORMATION
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
LTC4269-1
TO
16k
PSE
SHDN
V
PORTN
SIGNATURE DISABLE
Figure 3. 25k Signature Resistor with Disable
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
Table 2. Summary of Power Classifi cations and LTC4269-1
R
Resistor Selection
CLASS
CLASS
USAGE
0
Type 1
1
Type 1
2
Type 1
3
Type 1
4
Type 2
.
PORTN
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
V
PORTP
communicating over the high speed data line (layer 2). A
25k SIGNATURE
Type 2 PD must recognize both layers of communication.
RESISTOR
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.
42691 F03
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
that is chosen
CLASS
falls below undervoltage lockout threshold.
MAXIMUM
NOMINAL
LTC4269-1
POWER LEVELS
CLASSIFICATION
R
CLASS
AT INPUT OF PD
LOAD CURRENT
RESISTOR
(W)
(mA)
(Ω, 1%)
0.44 to 12.95
< 0.4
Open
0.44 to 3.84
10.5
124
3.84 to 6.49
18.5
69.8
6.49 to 12.95
28
45.3
12.95 to 25.5
40
30.9
. The T2P
PORTN
42691fb

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