5
dc2541af
DEMO MANUAL DC2541A
operation
application, these should be sized to accommodate system
surge level requirements. Across the LTC4279 AGND pin
and VEE pin are a local SMAJ58A, 58V TVS (D1) and a
1μF, 100V bypass capacitor (C4) component, both placed
close to the LTC4279 pins. An S1B standard rectifier diode
(100V, 1A) provides reverse polarity protection at the port
output as shown at D3 on the DC2541A.
Kelvin Sense
Proper connection of the port current sense lines is impor-
tant for current threshold accuracy and IEEE compliance.
On the DC2541A, the LTC4279 VSSK pin is connected to
a Kelvin sense trace that leads to the sense resistor pad
as shown in Figure 2 and is not connected directly to
VEE copper areas. Similarly, the LTC4279 SENSE pin is
connected to a Kelvin sense trace that leads to the sense
resistor pad and is not connected in the power path be-
tween the sense resistor and the MOSFET. The LTC4279
VEE pins and the sense resistor VEE pad connect to the
VEE copper areas.
Figure 2. DC2541A Kelvin Sense
Recommended Component Selection
The DC2541A power path components (RS1, Q1, and
T1) are chosen to accommodate all power levels up to
LTPoE++ 90W. In the end application, these components
can be optimized for the respective power level as listed
in Table 2.
Table 2. Recommended Power Path and Setting Components for the Various Power Levels
Power Level
Type 1
(13W)
Type 2
(25.5W)
LTPoE++
(38.7W)
LTPoE++
(52.7W)
LTPoE++
(70W)
LTPoE++
(90W)
Power Mode
Resistor (R
PM
)
2.37k, 1%
3.32k, 1%
4.64k, 1%
5.90k, 1%
7.87k, 1%
10.0k, 1%
Sense Resistor
(RS1)
0.1Ω, 1%, 1/10W,
±200ppm/°C
0.1Ω, 1%, 1/10W,
±200ppm/°C
0.1Ω, 1%, 1/4W,
±200ppm/°C
0.1Ω, 1%, 1/2W,
±200ppm/°C
0.1Ω, 1%, 1/2W,
±200ppm/°C
0.1Ω, 1%, 1W,
±200ppm/°C
Ethernet
Transformer (T1)
Würth 749023015
Würth 749022017
Würth 749022016,
Coilcraft ETH1-460L
Würth 749022016,
Coilcraft ETH1-460L
Würth 749022016,
Coilcraft ETH1-460L
Würth 749022016,
Coilcraft ETH1-460L
MOSFET (Q1)
NXP
PSMN075-100MSE
NXP
PSMN075-100MSE
NXP
PSMN040-100MSE
NXP
PSMN040-100MSE
NXP
PSMN040-100MSE
NXP
PSMN040-100MSE
