Demonstration Circuit 1682B Operation - Analog Devices DC1840C Demo Manual

DEMONSTRATION CIRCUIT 1682B OPERATION

12-Port PSE Daughter Card with Digital Isolation
Demonstration circuit 1682B (Figure 5) features the
LTC4270/LTC4271 chipset on a compact daughter card
with digital isolation. The LTC4270/LTC4271 chipset is
a 12-port power sourcing equipment (PSE) controller
designed for use in IEEE 802.3at Type 1 and Type 2 (high
power) compliant Power over Ethernet (PoE) systems. A
transformer isolated communication protocol replaces
expensive opto-couplers and complex isolated 3.3V supply
resulting in significant BOM cost savings. The LTC4270/
LTC4271 chipset delivers lowest-in-industry heat dissipa-
tion by utilizing low R external MOSFETs and 0.25Ω sense
ON
resistors, eliminating the need for expensive heat sinks.
Advanced power management features in the LTC4270/
LTC4271 chipset include: per port 12-bit current monitor-
ing ADCs, DAC programmable current limit, and versatile
quick shutdown of preselected ports. PD discovery uses a
Figure 5. DC1682B 12-Port PSE Daughter Card with Digital Isolation Features the LTC4270 and LTC4271
DEMO MANUAL DC1840C
proprietary dual mode 4-point detection mechanism ensur-
ing excellent immunity from false PD detection. Midspan
PSEs are supported with 2-event classification and a two
second backoff timer. The LTC4270/LTC4271 includes an
2
I C serial interface operable up to 1MHz.
The DC1682B demonstrates proper LTC4270/LTC4271
board layout that is approximately the height and width
of a 2 × 6 RJ45 connector. The compact layout is made
possible by the small package size of key components. The
LTC4270 is in a 7mm × 8mm QFN, while the LTC4271 is in
a 4mm × 4mm QFN. Each port has a PSMN075-100MSE
MOSFET in a 3mm × 3mm LFPAK33 package.
The daughter card inserts in the DC1680B mother board
through J1, a polarized 34-pin connector. Isolated 3.3V
and logic control signals are brought in on this connec-
tor. Also connected at J1 is the PoE V
mother board and 12 PSE controlled outputs.
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Rev E
5