LMX1214: design questions - discretes

Nandini Muralidharan

Part Number: LMX1214

Tool/software:

Hi,

1. In LMX1214EVM, all the PU and PD resistor values are 10K 0402 63mw. In datasheet table-7, it is given that CLKx_EN are to be tied to VCC with 1K in case it's used. Is 10K PU to VCC acceptable?

2. Can the PU and PD resistors for DIVSEL, MUXSEL be 10K?

3. In case CLKOUT is unused, to terminate it we are keeping 100nF AC cap and 50-ohm PD. Is 80mW sufficient for 50 ohms?

4. Clk buffer input is 1800MHz and CLKOUT is 225MHz LVDS to FPGA. AC-cap is currently set to 100nF. Is this ok? Or would you suggest any value in pF range instead?

Thanks

11 months ago

0 Noel Fung 11 months ago

TI__Guru** 108130 points

Hi Nandini,

10kΩ PU/PD is acceptable.

Unused CLKOUT could be disabled using the CLKx_EN pin. Output could be floating, I think AC short to ground is not necessary.

100nF at input is fine. Output is LVDS, then it should DC-coupled to the FPGA.

0 Nandini Muralidharan 11 months ago in reply to Noel Fung

Intellectual 810 points

Hi Noel,

1. Unused CLKOUT - we want to provide series capacitor with 50-ohm termination as outlined in datasheet. I plan to use 80mW rated resistor. Hope no concerns with the power rating.

2. FPGA input characteristics are highlighted. Based on this, I think we need to AC-couple the signals. Is my understanding correct?

0 Noel Fung 11 months ago in reply to Nandini Muralidharan

TI__Guru** 108130 points

Hi Nandini,

1. resistor rating is fine.

2. LVDS is usually DC-couple. Looks like the FPGA supports both AC and DC couple LVDS. My suggestion is DC couple.

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LMX1214: design questions - discretes