ltc4267cgn-1 Linear Technology Corporation, ltc4267cgn-1 Datasheet - Page 10

• Manufacturer Part Number: ltc4267cgn-1
• Description: Power Over Ethernet Ieee 802.3af Pd Interface With Integrated Switching Regulator
• Manufacturer: Linear Technology Corporation

LTC4267-1
APPLICATIO S I FOR ATIO
avoid corrupting the 25k signature resistor while also sav-
ing board space and cost. In addition, the inrush current
limit requirement of the IEEE 802.3af standard can cause
large transient power dissipation in the PD. The LTC4267-1
is designed to allow multiple turn-on sequences without
overheating the miniature 16-lead package. In the event of
excessive power cycling, the LTC4267-1 provides thermal
overload protection to keep the onboard power MOSFET
within its safe operating area.
OPERATION
The LTC4267-1 PD interface has several modes of opera-
tion depending on the applied input voltage as shown in
Figure 1 and summarized in Table 1. These modes satisfy
the requirements defi ned in the IEEE 802.3af specifi cation.
The input voltage is applied to the V
be negative relative to the V
sheet for the PD interface portion of the LTC4267-1 are
with respect to V
ing regulator are referenced to PGND. It is assumed that
PGND is tied to P
symbols throughout the data sheet.
Table 1. LTC4267-1 Operational Mode
as a Function of Input Voltage
INPUT VOLTAGE
(V
0V to – 1.4V
–1.5V to –9.5V**
–9.8V to –12.4V
–12.5V to UVLO*
UVLO* to –57V
**Measured at LTC4267-1 pin. The LTC4267-1 meets the IEEE 802.3af 10V
10
*V
PORTN
Rising input threshold ≅ – 36.0V
Falling input threshold ≅ –30.5V
minimum when operating with the required diode bridges.
PORTN
with RESPECT to V
UVLO includes hysteresis.
PORTP
OUT
U
PORTP
. Note the use of different ground
while the voltages for the switch-
) LTC4267-1 MODE OF OPERATION
U
PORTP
Inactive
25k Signature Resistor Detection
Classifi cation Load Current Ramps up
from 0% to 100%
Classifi cation Load Current Active
Power Applied to Switching Regulator
pin. Voltages in the data
W
PORTN
pin and must
U
Figure 1. Output Voltage, ⎯ P ⎯ W ⎯ R ⎯ G ⎯ D and PD
Current as a Function of Input Voltage
42671f