ltc4267-3 Linear Technology Corporation, ltc4267-3 Datasheet - Page 18

• 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
designer should determine which power category the PD
falls into and then select the appropriate value of R
from Table 2. If a unique load current is required, the value
of R
where I
classifi cation and is given in the electrical specifi cations.
The R
18
APPLICATIO S I FOR ATIO
R
CLASS
CLASS
CLASS
IN_CLASS
can be calculated as:
= 1.237V/(I
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RESISTORS ARE 5%
2. SELECT R
C2: AVX 1808GC102MAT
D9 TO D12, D14 TO D17: DIODES INC., B1100
T1: PULSE H2019
TO DATA SHEET APPLICATIONS INFORMATION SECTION
resistor must be 1% or better to avoid de-
is the LTC4267-3 IC supply current during
FROM
PSE
IN
CLASS
U
RJ45
DESIRED
J2
FOR CLASS 1-4 OPERATION. REFER
4
5
7
8
1
2
3
6
TX
TX
RX
RX
Figure 10. PD Front End with Isolation Transformer, 2nd Schottky Diode Bridge
U
+
–
+
–
SPARE
SPARE
– I
16
15
14
11
10
0.01µF
9
200V
+
–
IN_CLASS
75Ω
C3
R2
T1
W
1
2
3
6
7
8
)
TO PHY
TXOUT
TXOUT
RXOUT
RXOUT
C2
1000pF
2kV
OUT
R1
75Ω
C7
0.01µF
200V
+
–
+
–
U
B1100
C25
0.01µF
200V
CLASS
D9
R31
75Ω
B1100
B1100
D17
D10
B1100
D15
C24
0.01µF
200V
R30
75Ω
grading the overall accuracy of the classifi cation circuit.
Resistor power dissipation will be 50mW maximum and
is transient so heating is typically not a concern. In order
to maintain loop stability, the layout should minimize
capacitance at the R
can be disabled by fl oating the R
should not be shorted to V
LTC4267-3 classifi cation circuit to attempt to source very
large currents and quickly go into thermal shutdown.
B1100
B1100
B1100
D12
D16
D14
B1100
D11
R
1%
CLASS
D6
SMAJ58A
CLASS
R
V
PORTN
CLASS
LTC4267-3
MMSD4148
node. The classifi cation circuit
PORTN
V
PORTP
C11
0.1µF
100V
D13
CLASS
as this would force the
42673 F10
pin. The R
CLASS
42673f
pin