78P2351-DB/ECLM Maxim Integrated Products, 78P2351-DB/ECLM Datasheet - Page 4

• Manufacturer Part Number: 78P2351-DB/ECLM
• Description: BOARD DEMO 78P2351 W/OPT MODULE
• Manufacturer: Maxim Integrated Products

Specifications of 78P2351-DB/ECLM

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Design Guidelines for TERIDIAN 78P235x LIUs
All CMI coded (Analog) differential pair signal routes should have a differential trace impedance of 75
the 78P235x IC and the transformer. The termination resistors need to be placed as close as possible, and within
one inch, of their 78P235x pins to optimize transmit pulse shaping and minimize reflections.
The transmit and receive ‘Tip’ (on primary side of transformer) should be a
connector. The coax shield or ‘Ring’ should be directly connected to the frame or chassis ground plane.
quality of this ground connection is critical for ESD Immunity at the faceplate and EMC performance.
Unlike the CMI Receiver, the Transmitter requires external biasing. Figure 5 shows two methods for biasing the
transmit driver. Biasing the transmit path at the transformer center tap with a single 75Ω termination resistor uses
the fewest components, but is only recommended when the transformer placement can be near the LIU.
The alternate (and preferred) method is to bias the transmit path between the 2 termination resistors minimizing
the path and inductance from Vcc to the internal current sink. The value of each resistor should equal to one half
of the total termination used for the pair, so that each half of the signal is seeing the correct termination value
(37.5Ω). The decoupling capacitor value should be 0.1uF (or a combination of 0.01uF and 0.1uF).
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RING
RING
RX CMI Input
RING
TIP
TIP
TIP
Figure 5: CMI Transmitter (Transformer and Resistor Biasing options)
TX CMI Output
TX CMI Output
(Transformer Bias)
(Resistor Bias)
75 ohm
75 ohm
75 ohm
 2008 Teridian Semiconductor Corp.
0.1uF
Figure 4: CMI Receiver
VCC
37.5 ohm
37.5 ohm
37.5 ohm
37.5 ohm
37.5 ohm
37.5 ohm
VCC
0.1uF
75
37.5
< 1"
< 1"
< 1"
PCB
PCB
75
PCB
37.5
CMIxN
CMIxN
235x IC
CMIxP
CMIxP
RXxP
235x IC
RXxN
235x IC
10k
10k
26mA
26mA
75
Ω
single-ended trace
to gates
to gates
2.1V
circuit
circuit
from
from
to the coax
Ω
between
Rev 2.1
The