Analog Devices DC2685B-KIT Demo Manual page 5

DEMONSTRATION CIRCUIT 2684A-B DAUGHTER CARD
Demonstration circuit 2684A-B is an IEEE 802.3bt 8-chan-
nel PSE daughter card that features the LTC4291-1/
LTC4292 chipset. This daughter card mates with a 4-Port,
4-Pair PoE motherboard for use in IEEE 802.3bt Type 3 or
4 compliant Power over Ethernet PSE systems.
Board Layout
Parts placement, sense resistor block and Kelvin sens-
ing, copper fill, trace routing, and spacing are crucial
for LTC4291-1/LTC4292 chipset operation, robustness,
and measurement accuracy. It is imperative to follow
the layout requirements specified in the LTC4291-1/
C21
0.1µF
V
DD33
CPD
U2
LTC4291-1
C23
1µF
CND
DPD
C22
1µF
DND
DGND
WÜRTH 7490100143
V
DD
T1
– –
RX RD
R13 R21
100 100
CT(4) CT(3)
R14 R22
100 100
+ +
RX RD
– –
TX TD
R15 R23
100 100
CT(2) CT
R16 R24
100 100
+ +
TX TD
C24, 2.2nF
2kV
V
V
EE
Figure 4. DC2684A-B Digital and Analog Isolation
LTC4292 data sheet. The DC2684A-B demonstrates
proper LTC4291-1/LTC4292 board layout on a compact
daughter card approximately the height and width of a 2
× 4 RJ45 connector.
Isolation and Power Supplies
The LTC4291-1/LTC4292 chipset provides communica-
tion across an isolation barrier through a data transformer
(Figure 4). All digital pins reside on the digital ground
reference and are isolated from the analog PoE supply on
the daughter card layout. A V
supply is brought in at the 30-pin connector J1.
DC2684 SIDE
CPA
U1
LTC4292
AGNDP
C19
CNA
1µF
100V
DPA
V
EE
DNA
EE
ISOLATION
DEMO MANUAL
DC2685B-KIT
logic supply and V
DD
30-PIN
CONNECTOR
MOTHERBOARD SIDE
+
V SUPPLY
–
DD
R35
10
+
C
BULK
D1
TVS
TVS, 58V
DC2685B F04
PoE
EE
+
V SUPPLY
–
EE
BULK
Rev. B
5