LTC4265IDE#PBF Linear Technology, LTC4265IDE#PBF Datasheet - Page 7

• Manufacturer Part Number: LTC4265IDE#PBF
• Description: IC CTRLR PD INTERFACE HP 12-DFN
• Manufacturer: Linear Technology
• Type: Power over Ethernet Switch (PoE)r

Specifications of LTC4265IDE#PBF

• Applications: Remote Peripherals (Industrial Controls, Cameras, Data Access)
• Internal Switch(s): Yes
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 12-WFDFN Exposed Pad
• Input Voltage: 60V
• Supply Current: 1.35mA
• Digital Ic Case Style: DFN
• No. Of Pins: 12
• Uvlo: 30V
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Termination Type: SMD
• Rohs Compliant: Yes
• Filter Terminals: SMD
• Controller Type: Hot Swap
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
These modes satisfy the requirements defi ned in the IEEE
802.3af/at specifi cation.
Table 1. LTC4265 Modes of Operation as a Function
of Input Voltage
GND (V)
0V to 1.4V
1.5V to 9.8V
(5.4V to 9.8V)
12.5V to ON/UVLO* Classifi cation Load Current Active
ON/UVLO* to 60V
>71V
*ON/UVLO includes hysteresis. Rising input threshold, 37.2V Max.
Falling input threshold, 30V Min.
INPUT DIODE BRIDGE
In the IEEE 802.3af/at standard, the modes of operation
reference the input voltage at the PD’s RJ45 connector.
Since the PD must handle power received in either polarity
from either the data or the spare pair, input diode bridges
BR1 and BR2 are connected between the RJ45 connector
and the LTC4265 (Figure 2).
LTC4265 MODES OF OPERATION
Inactive (Reset After 1st Classifi cation Event)
25k Signature Resistor Detection Before 1st
Classifi cation Event (Mark, 11k Signature
Corrupt After 1st Classifi cation Event)
Inrush and Power Applied To PD Load
Overvoltage Lockout, 4265 Operations are Disabled
DEVICE (PD)
POWERED
Figure 2. PD Front End Using Diode Bridges on Main and Spare Inputs
INPUT
RJ45
1
2
3
6
4
5
7
8
TX
TX
RX
RX
+
–
+
–
SPARE
SPARE
+
–
T1
BR2
TO PHY
The input diode bridge introduces a voltage drop that
affects the range for each mode of operation. The LTC4265
compensates for these voltage drops so that a PD built with
the LTC4265 meets the IEEE 802.3af/at-established voltage
ranges. Note that the Electrical Specifi cations reference
with respect to the LTC4265 package pins.
DETECTION
During detection, the PSE looks for a 25k signature resis-
tor which identifi es the device as a PD. The PSE will apply
two voltages in the range of 2.8V to 10V and measures
the corresponding currents. Figure 1 shows the detection
voltages V1 and V2 and the corresponding PD current. The
PSE calculates the signature resistance using the ΔV/ΔI
measurement technique.
The LTC4265 presents its precision, temperature-compen-
sated 25k resistor between the GND and V
the PSE that a PD is present and requests power to be
applied. The LTC4265 signature resistor also compensates
for the additional series resistance introduced by the input
diode bridge. Thus a PD built with the LTC4265 conforms
to the IEEE 802.3af/at detection specifi cations.
0.1μF
100V
BR1
D3
V
IN
LTC4265
GND
4265 F02
LTC4265
IN
pins, alerting
4265fa
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