lm4312 National Semiconductor Corporation, lm4312 Datasheet - Page 17

• Manufacturer Part Number: lm4312
• Description: Mobile Pixel Link Two Mpl-2 , Rgb Display Differential Interface Serializer With Optional Dithering And Look Up Table
• Manufacturer: National Semiconductor Corporation

FLEX CIRCUIT RECOMMENDATIONS
The MPL-2 lines should generally run together to minimize
any trace length differences (skew). For impedance control
and also noise isolation (crosstalk), guard ground traces are
recommended in between the signals. Commonly a Ground-
Signal-Signal-Ground (GSSGSSG) layout is used. Locate
fast edge rate and large swing signals further away to also
minimize any coupling (unwanted crosstalk). In a stacked flex
interconnect, crosstalk also needs to be taken into account in
the above and below layers (vertical direction). To minimize
any coupling locate MPL-2 traces next to a ground layer.
Power rails also tend to generate less noise than LVCMOS
so they are also good candidates for use as isolation and
separation.
The interconnect from the SER to the DES may act like a
transmission line. Thus impedance control and ground re-
turns are an important part of system design. Impedance
should be in the 80 to 100 Ohms for the differential pair.
GROUNDING
The LM4312 offered in the 48 LLP package uses the center
DAP Pad for the Ground connection. This pad MUST be con-
nected to Ground for proper device operation.
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PCB RECOMMENDATIONS
General guidelines for the PCB design:
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Floor plan - locate MPL-2 SER near the connector to limit
chance of cross talk to high speed serial signals.
Route serial traces together, minimize the number of layer
changes to reduce loading.
Use ground lines as guards to minimize any noise coupling
(guarantees distance).
Avoid parallel runs with fast edge, large LVCMOS swings.
Also use a GSSG pinout in connectors (Board to Board or
ZIF).
DES device - follow similar guidelines.
Bypass the device with MLC surface mount devices and
thinly separated power and ground planes with low
inductance feeds.
High current returns should have a separate path with a
width proportional to the amount of current carried to
minimize any resulting IR effects.
See AN-1187 LLP Package Application Note for SMT
Assembly Recommendations
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