CDC328A: Driving 50Ω coax line

Jejomar Ildefonso

Part Number: CDC328A
Other Parts Discussed in Thread: CDC329A

Hi Team,

Asking your expertise on our customer's query. They need to drive nominal TTL or 5V COMS levels into possibly a worst case 50Ω terminated cable. Are the CDC329A and CDC328A clock buffers suitable for this? Would it be recommended to parallel 2 or 3 CDC328A or CDC329A outputs to accomplish this?

If there's a better option to achieve their requirement, we would really appreciate your inputs as well.

Thanks in advance!

Kind Regards,

Jejomar

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru* 87510 points

Hi Jejomar,

How many output is needed and how long is the cable?

Do you expect to see 5V on the 50Ω load at the receiving side?

0 Jejomar Ildefonso over 3 years ago in reply to Noel Fung

TI__Expert 8790 points

Hi Noel,

Many thanks for checking into this. Our customer does not expect the cable to be terminated at the 50 Ohm end to +5 V. It will be terminated either to an open circuit, an RC 50Ω - 1000 pF series termination to ground, or to 50Ω to ground. The cable length is approximately 12 feet. We are considering using 3 outputs in parallel to provide 96 mA available current - - each output isolated from each other with a nominal 50 Ω resistor for current sharing and current limiting during the switch transition. Does this seem reasonable?? The 50 Ohm sharing resistors may be adjusted to make sure we can get a valid logical high voltage level at the load into a 50 Ohm termination.

Would two gate functions in parallel be considered reasonable for this application?

Kind Regards,

Jejomar

0 Noel Fung over 3 years ago in reply to Jejomar Ildefonso

TI__Guru* 87510 points

Hi Jejomar,

I think it will work in this way but it would be good to confirm the outcome with a simulation.

We have spice model for this part, maybe the customer can do a sim to confirm.

0 Jejomar Ildefonso over 3 years ago in reply to Noel Fung

TI__Expert 8790 points

Hello Noel,

We would gladly propose a simulation to the customer. Can you share with us the spice model? We can't locate it for CDC328A while the CDC329A only has IBIS model.

Kind Regards,

Jejomar

0 Jejomar Ildefonso over 3 years ago in reply to Jejomar Ildefonso

TI__Expert 8790 points

Hi Noel,

May we ask for a follow-up on this? Thanks in advance!

Kind Regards,

Jejomar

0 Noel Fung over 3 years ago in reply to Jejomar Ildefonso

TI__Guru* 87510 points

Hi Jejomar,

You are right, I think I messed up the parts, there is no spice or IBIS model for 328A.

Maybe the customer can consider 329A, the difference between 328A and 329A is not big.

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CDC328A: Driving 50Ω coax line