The DS90UB953-Q1 EVM platform can be used to evaluate TSER953. The board layout for the DS90UB953-Q1 EVM is shown in Figure 10-1 and Figure 10-2. All EVM layers are included in DS90UB953-Q1 EVM user's guide (SNLU224).
Routing the V3Link signal traces between the DOUT pins and the connector, as well as connecting the PoC filter to these traces, are the most critical pieces of a successful TSER953 PCB layout. The following list provides essential recommendations for routing the V3Link signal traces between the driver output pins and the FAKRA connector, as well as connecting the PoC filter.
- The routing of the V3Link traces may be all on the top layer or partially embedded in middle layers if EMI is a concern.
- The AC-coupling capacitors should be on the top layer and very close to the receiver input pins to minimize the length of coupled differential trace pair between the pins and the capacitors.
- Route the DOUT+ trace between the AC-coupling capacitor and the FAKRA connector as a 50-Ω single-ended micro-strip with tight impedance control (±10%). Calculate the proper width of the trace for a 50-Ω impedance based on the PCB stack-up. Ensure that the trace can carry the PoC current for the maximum load presented by the remote sensor module.
- The PoC filter should be connected to the DOUT+ trace through the ferrite bead or an RF inductor. The ferrite bead should be touching the high-speed trace to minimize the stub length seen by the transmission line. Create an anti-pad or a moat under the ferrite bead pad that touches the trace. The anti-pad should be a plane cutout of the ground plane directly underneath the top layer without cutting out the ground reference under the trace. The purpose of the anti-pad is to maintain the impedance as close to 50 Ω as possible.
- When routing DOUT+ on inner layers, length matching for single-ended traces does not provide a significant benefit. If the user wants to route the DOUT+ on the top or bottom layer, route the DOUT– trace loosely coupled to the DOUT+ trace for the length similar to the DOUT+ trace length. This may help the differential nature of the receiver to cancel out any common-mode noise that may be present in the environment that may couple on to the signal traces.
Figure 10-1 TSER953 Serializer DOUT+ Trace Layout Figure 10-2 TSER953 Power-over-Coax Layout