LMX2592EVM: LMX2592 impedance of OSCin

Jerry Huang

Prodigy 10 points

Part Number: LMX2592EVM
Other Parts Discussed in Thread: LMX2592

Hi,

I check the schematic of LMX2592EVM, the OSCin pin have stuffed external 3 resistance.

Is the function of those resistance for input impedance control?

I have check LMX2592 datasheet, and it point out the looking outward of OSCin pin should close to 50OHM.

May I know why LMX2592EVM design with 18 and 68 OHM?

Thanks,

Jerry

over 2 years ago

+1 Ajeet Pal over 2 years ago

TI__Genius 12550 points

Hi Jerry,

The resistors combination of 18 ohm & 68 ohm are the T-pad attenuator for 6dB attenuation on OSCin path. Here, R14 and R14p are the shared pad components (any one of the resistor would use). When single ended external input is present, keep R14 and remove R14p and terminate 50ohm at OSCinM connector. Similarly, when on-board oscillator is present, keep R14p on board and remove R14, Also terminate 50ohm at OSCinM connector.

Regards,

Ajeet Pal

0 Jerry Huang over 2 years ago in reply to Ajeet Pal

Prodigy 10 points

Hi Ajeet

Thanks for answering.

As my under understanding, if we can make sure Vppd of input signal under 1 volt. Then we can remove the T-pad attenuator and shunt 50OHM resistor for termination. Is it correct?

Thanks,

Jerry

+1 Ajeet Pal over 2 years ago in reply to Jerry Huang

TI__Genius 12550 points

Hi Jerry,

Yes, if OSCIn input level is within the range mentioned in datasheet, T-pad attenuator can be remove.

Regards,

Ajeet Pal

0 Jerry Huang over 2 years ago in reply to Ajeet Pal

Prodigy 10 points

Hi Ajeet

Thanks for your answer. That is really helpful.

Jerry

Clock & timing

Clock & timing forum

LMX2592EVM: LMX2592 impedance of OSCin