LMX2492EVM: Resistor R12 for RFout/4

Darryn Jordan

Part Number: LMX2492EVM

Hi All,

Please could anyone advise as to whether one should populate resistor R12 if RFout/4 is going to be used?

I want to use RFout/4 in a 50 ohm system and R12 seems to be needed for a 50 ohm tee network? The board is however shipped without it.

I assume the output impedance of the RFVC1843 is 100 ohm (from Fo/4), which would correspond to the chosen values for resistors R11 (18 ohm), R12 (68 ohm) and R13 (18 ohm)?

If these assumptions are correct, do we expect a 10 dB drop in output power? The power out of RFout/4 would then be approx -12 dBm?

Please let me know if I'm completely off the mark?

Kind Regards

Darryn Jordan

over 6 years ago

0 Brian Wang over 6 years ago

TI__Expert 7845 points

Hi Darryn,

The T pad you see is intended to be a placeholder so that user can tune the resistor network on the EVM and set to preferred impedances.

Regards,

Brian Wang

0 Darryn Jordan over 6 years ago in reply to Brian Wang

Prodigy 130 points

Hi Brian!

Thanks for your response.

If R12 is not populated with any resistor - is the output impedance of the RFout/4 port 50 ohms? and what output power can be expected from RFout/4?

Kind Regards
Darryn

0 Noel Fung over 6 years ago in reply to Darryn Jordan

TI__Guru* 81230 points

Hi Darryn,

From the VCO datasheet, RFout/4 output power is -1.5dBm. However, datasheet did not tell the impedance of each output port.

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LMX2492EVM: Resistor R12 for RFout/4