Routing the CSI-2 signal traces
between the CSI-2 pins and the CSI-2 connector is also important for a successful
TDES954 PCB layout. Figure 10-3 shows essential
details for routing the CSI-2 traces. Additional recommendations are given in the
following list:
- Route CSI_D0N, CSI_D0P, CSI_D1N,
and CSI_D1P pairs as differential coupled striplines with controlled 100-Ω
differential impedance (±10%)
- Keep the trace length difference
between CSI-2 traces to 5 mils of each other.
- Length matching should be near
the location of mismatch.
- Each pair should be separated at
least by 5 times the signal trace width.
- Keep away from other high-speed
signals.
- Keep the use of bends in
differential traces to a minimum. When bends are used, the number of left and
right bends must be as equal as possible, and the angle of the bend should be ≥
135 degrees. This arrangement minimizes any length mismatch caused by the bends
and therefore minimizes the impact that bends have on EMI.
- Route all differential pairs on
one or two inner layers.
- Keep the number of signal vias to
a minimum — TI recommends keeping the via count to the maximum of two per CSI-2
trace.
- Keep traces on layers adjacent to
ground plane.
- Do NOT route differential pairs
over any plane split.
- Adding Test points causes
impedance discontinuity and therefore negatively impacts signal performance. If
test points are used, place them in series and symmetrically. Test points must
not be placed in a manner that causes a stub on the differential pair.