Hi Team,
Good day. Can you please help with the inquiry below?
A customer use LMX2492 + CHC2442 to generate 24G source signal, originally, 40MHz TCXO feeding to LMX2492, works well for 24GHz source signal generation. However, when they switch to 100MHz VCXO feeding to LMX2492, they could not functionally be operating that the output signal is unlocked.
For debugging, the customer use SG as OSCin, it is found that OSCin frequency is less than 80MHz, it could work well, but LMX2492 could not lock the output when OSCin frequency is higher than 80MHz. They TI official software tool for LMX2492 configuration, it should be OK for REGs setup. on datasheet, LMX2492 OSCin could be lower than 600MHz, REGs OK, 100MHz OSCin, but LMX2492 could not lock the output, while works well when OSCin below 80MHz.
I suggest that the customer check if POWERDOWN bit was set correctly and they mentioned that it is set as 0x01. Further investigation suggested that if LMX2492 PD frequency is set as 50MHz, the OSCin could be 100MHz, even 200MHz. VCO output frequency could be locked. but if LMX2492 PD frequency is set as 100MHz, the Max OSCin is 85MHz, higher than that, CPout is measured as highest voltage so as not to lock the output frequency.
Would you kindly help further?
Thanks!
Regards,
Marvin
