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LMH1297: PCB layout

Emanuel Cohen
Prodigy 50 points
Part Number: LMH1297

Hello,

Can u pls. advise for the PCB layout for the LMH1297.

 My  PCB stuck-up is : 

1-CS. Signal 

2. Ground/Power Plane

3. Signal 

4. Ground/Power Plane

5. Signal 

6. Ground/Power Plane

7. Signal 

8. Ground/Power Plane

9. Signal 

10. Ground/Power Plane

11. Ground/Power Plane

12. Signal 

13. Ground/Power Plane

14. Signal 

15. Ground/Power Plane

16. Signal 

17. Ground/Power Plane

18. Signal

19. Ground/Power Plane

20-PS. Signal 

I planning to place the LMH1297 on the print side (layer  20) and rout the 75 Ohm signals (SDI_IO+/-) on layer 20, making a void under them at layer 19 and 18,  and use layer 17 as a reference Plane for the 75 Ohm traces,do u recommend it?

Also, is it OK if I use layer 18 as reference plane, for the 75 ohm traces at  layer 20 ? I am planning to do so by creating a void at layer 19 and implement  a small plane area under the 75 Ohm traces, at layer 18  that will be connect it to ground layer 19 by VIAS).

Best regards,

Emanuel

  • 0
    TI__Guru* 93670 points

    Hi Emanuel,

    This depends on your board stack up. LMH1297 EVM has 6 layers pcb. Layer 1 is used to route both 100- ohm and 75-ohm traces. For 100-ohm differential signal layer 2 is the referenced layer. Given our board material, trace width is 10mils. For 75-ohm trace, layer 3 is the referenced layer and it is 8 mils. Please consult your pcb vendor and pcb layout designer to achieve 75 and 100-ohm trace impedance given your board stack up/material. There is also different software for calculating trace impedance. For example, you can check Saturn or Agilent ADS software.

    Also, we can provide you with LMH1297EVM pcb layout so you can use this as guideline as well. Please use your company email address and send me email to request this document Here is my email address: nasser.mohammadi@ti.com.

    Regards,, Nasser