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TMS320DM368 interface with TFP410

Ashwani
Expert 1365 points

Other Parts Discussed in Thread: TFP410, TMS320DM368

Hi,

I am interfacing TFP410 with TMS320DM368 digital video output port. I have the following queries:

TMS320DM368

1. TMS320DM368 data sheet recommends on (page-21):
    “To reduce EMI and reflections, depending on the trace length, approximately 22 Ω to 50 Ω damping resistors are recommend on
     the following outputs placed near the device: YOUT(0-7),COUT(0-7), HSYNC, VSYNC, LCD_OE, FIELD, and VCLK.”
     Is the above damping resistors included PCB trace impedance? i.e. if PCB trace impedance is 10 Ω then damping resistors may
     be 12 Ω to 40 Ω ?

2. What about the other Digital Video RGB signals (GIO33, GIO32, GIO30, GIO29, GIO80, GIO28 and GIO27), do these signals are also require  damping resistors?

 

  • 0
    TI__Expert 6850 points

    First off, PCB trace impedance of 10 Ohm seems to be impractical. For the entire bus to be done this way (10 Ohm trace), it would take an enormous amount of PCB space. Perhaps this is DC resistance?  DC resistance doesn’t really factor into the equation since it’s rarely more than 1 ohm.  The thinnest trace (4 mils for any length outside the BGA area) is 2.5 ohms for a 10 inch trace, so a 10 ohm trace must be measured wrong. 

    Traces should always be designed to be as close to the buffer impedance as possible, usually 45-65 ohms. As far as practical resistance values, it’s best if the trace impedance = buffer impedance + termination resistance.  In practice, it doesn’t seem to matter much what they are, the difference is pretty small.  Usually about 20-33 ohms is used for typical traces.

  • 0 in reply to Jeff Hayes
    TI__Expert 5955 points

    Hi,

    Addition to Jeff's response and answer the second question, on a reference design, as the analog RGB signals that go to the VGA connector, we use a standard parallel termination used for analog video signals.

    Thanks.

    -Tai