ltc4267-3 Linear Technology Corporation, ltc4267-3 Datasheet - Page 10

• Manufacturer Part Number: ltc4267-3
• Description: Power Over Ethernet Ieee 802.3af Pd Interface With Integrated 300khz Switching Regulator
• Manufacturer: Linear Technology Corporation

LTC4267-3
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 LTC4267-3
is designed to allow multiple turn-on sequences without
overheating the miniature 16-lead package. In the event of
excessive power cycling, the LTC4267-3 provides thermal
overload protection to keep the onboard power MOSFET
within its safe operating area.
OPERATION
The LTC4267-3 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 LTC4267-3 are
with respect to V
regulator are referenced to PGND. It is assumed that PGND
is tied to P
throughout the data sheet.
Table 1. LTC4267-3 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 LTC4267-3 pin. The LTC4267-3 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.
OUT
. Note the use of different ground symbols
PORTP
U
PORTP
while the voltages for the switching
) LTC4267-3 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
PSE
I
LIM_LO
I
CLASS
– 20
– 30
– 40
– 50
– 10
– 20
– 30
– 40
– 50
– 10
– 20
– 30
– 40
– 50
–10
Figure 1. Output Voltage, PWRGD and PD
Current as a Function of Input Voltage
V
I
I
I
IN
VOLTAGES WITH RESPECT TO V
I
I
LOAD
1
2
CLASS
LIM_LO
=
=
R
CLASS
V1 – 2 DIODE DROPS
V2 – 2 DIODE DROPS
I
dV
IN
UVLO
=
dt
OFF
DEPENDENT ON R
= 140mA (NOMINAL), I
R
=
V
POWER
DETECTION V1
LOAD
OUT
I
LIM_LO
BAD
DETECTION V2
DETECTION I
DETECTION I
C1
CLASSIFICATION
I
25kΩ
25kΩ
CLASS
CLASSIFICATION
(UP TO I
R
V
PORTN
CLASS
LTC4267-3
UVLO
TURN-ON
UVLO
POWER
ON
PWRGD
GOOD
V
LIM_HI
2
1
PORTP
PGND
CLASS
P
OUT
)
LIM_HI
SELECTION
PORTP
PWRGD TRACKS
V
CURRENT
LIMIT, I
UVLO
TURN-OFF
LOAD, I
PORTN
= R
POWER
= 375mA (NOMINAL)
UVLO
OFF
BAD
R9
LOAD
TIME
TIME
TIME
TIME
LIM_LO
LOAD
R
C1
LOAD
C1
(UP TO I
42673 F01
V
OUT
LIM_HI
)
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