LMK04906 lock issue

Maximilian Buechele

Other Parts Discussed in Thread: LMK04906

Hi,

I tried to launch the LMK04906 EVB but it seems that the PLLs don't lock. I can program different output clocks via the uwire interface, so in general the system seems to work. But looking on the LD_TP the PLL1/2 DLD signals are on ground. The PLL1_R/2 signal shows half the Phase Detector Frequency as expected. I also tried to use different high accuracy input clocks.

Strange to me is that the VCC VCXO_TP is on ground, too.

Thanks in advance,

Maximilian

over 11 years ago

0 Gabe Ayala over 11 years ago

TI__Genius 10320 points

Hi Maximilian,

Assuming you left the board in default configuration, do you see 3.3V on LDO_OUT_LP3837 Test Point?

Gabe

0 Alan O over 11 years ago

TI__Mastermind 32575 points

It sounds like the power supply to the VCXO is incorrect. Have you tried probing up the chain to see why? The LDO regulator used to power the VCXO is U305. Probe LDO side of R19 to see if you get 3.3V. If so, make sure R19 and R18 are installed with 0 ohms. If the U305 output is not 3.3V, then make sure the LDO input voltage is getting power by making sure R373, R364, and R332 are installed with 0 ohms.

Regards,
Alan

0 Maximilian Buechele over 11 years ago in reply to Alan O

Prodigy 30 points

Hi Alan,

I found out that the LDO powering the VCXO is broken. Shorting VCC_VCXO_TP and LDO_OUT_LP3837 to provide 3.3V to the VCXO solved the problem.

Thanks,

Maximilian

Clock & timing

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LMK04906 lock issue