LMK04832: CLKIN2 reference input unusable

itamar mazaki

Part Number: LMK04832

Hello,

My design uses LMK04832 in a dual loop configuration. I use CLKIN2 for 10MHz LVDS reference for PLL1. In this setup, PLL1 does not lock.

I have tried to repeat this setup on the LMK04832EVM, but PLL1 would lock only on clock inputs 0 and 1, but not on CLKIN2 (it is enabled, either MOS/Bipolar, output is in powerdown).

is there a special register sequence that will enable the use of this input?

I have repeated the test on LMK04828EVB, but got the same results.

also, when I try to see PLL1_R, PLL1_R/2, PLL1_R/4 on both components, I see something that looks like an output of a phase detector and not a divided reference.

Thanks

Itamar

over 5 years ago

0 Timothy T over 5 years ago

TI__Mastermind 28550 points

Hello Itamar,

On the EVM, did you reconfigure OSCout/CLKin2 for input? By default it has 240 ohm emitter resistors which would ground the input. Ideally you would also place a differential 100 ohm resistor for a differential input. If using a single ended input, a 50 ohm resistor to ground at R31 needs to be DC blocked by placing a capacitor at R33. Normally C65/C66 would provide DC block.

There is not special sequence except for disabling/powering down the OSCout and selecting CLKin2 as the input. Are you using manual mode?

If you are still having issues, could you post your saved. TCS file?

73,
Timothy

0 itamar mazaki over 5 years ago in reply to Timothy T

Prodigy 60 points

Hello Timothy,

I have replaced the serial jumper resistors on clkin2's input with capacitors, and now it is working perfectly.

Thank you for your help

Itamar

0 Timothy T over 5 years ago in reply to itamar mazaki

TI__Mastermind 28550 points

Great. Glad all is working for you. If you have any other questions, go ahead and start a new thread.

73,
Timothy

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LMK04832: CLKIN2 reference input unusable