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LMK61E08: Cannot adjust output/I2C disappears

Ryan Seeley
Prodigy 10 points
Part Number: LMK61E08

Tool/software:

We put the LMK61E08-SIAR on a PCB and we we able to turn it on and program it. The output frequency would not update. I have replaced the IC with a new IC. It was initially visible on I2C but after attempting to program it, it has disappeared. An suggestions on what might be happening? I can swap out the IC for a new one but it would be good to have some idea of what is going on and why we cannot get a programmed IC to output the frequency that we would like.

  • 0
    TI__Genius 12350 points

    Hi Ryan, 

    Can you scan the bus to see if the device responds to a different I2C address? It's possible that when you reprogrammed the EEPROM R8 was updated and changed the device's I2C address. Also, can you send over the register configuration that you programmed to the device? 

    Regards, 

    Connor 

  • 0 in reply to Connor Lewis
    Prodigy 10 points

    Hi Connor, 

    Thanks for the reply. Yes after you mentioned it, we did notice that the I2C address changed. We are still unable to get an output frequency. 

    Here is the register configuration:

    R0 0x0010
    R1 0x010B
    R2 0x0233
    R8 0x08FA
    R9 0x09FF
    R16 0x1000
    R17 0x1180
    R21 0x1501
    R22 0x1600
    R23 0x1720
    R25 0x1900
    R26 0x1A33
    R27 0x1B00
    R28 0x1C07
    R29 0x1DD0
    R30 0x1E00
    R31 0x1F27
    R32 0x2010
    R33 0x210C
    R34 0x2228
    R35 0x2303
    R36 0x2408
    R37 0x2500
    R38 0x2600
    R39 0x2700
    R47 0x2F67
    R48 0x3003
    R49 0x3150
    R50 0x32FE
    R51 0x3300
    R52 0x34FE
    R53 0x3505
    R56 0x3800
    R72 0x4800

    This is the register readout:

  • 0 in reply to Ryan Seeley
    TI__Genius 12350 points

    Hi Ryan, 

    Looking at R21, it looks like the device is configured for LVPECL. Do you have the proper LVPECL termination on your board? If you don't have emitter resistors in the DC path you may not be able to see an output. Here are some examples of valid LVPECL termination schemes:

    Regards, 

    Connor 

  • 0 in reply to Connor Lewis
    Prodigy 10 points

    HI Connor,

    We made some adjustments and set the output to be LVDS. There is still no output.

    R0 0x0010
    R1 0x010B
    R2 0x0233
    R8 0x08FA
    R9 0x09FF
    R16 0x1000
    R17 0x1180
    R21 0x1502
    R22 0x1600
    R23 0x171E
    R25 0x1900
    R26 0x1A30
    R27 0x1B00
    R28 0x1C00
    R29 0x1D00
    R30 0x1E00
    R31 0x1F00
    R32 0x2001
    R33 0x210C
    R34 0x2228
    R35 0x2303
    R36 0x2404
    R37 0x2500
    R38 0x2600
    R39 0x2700
    R47 0x2FC3
    R48 0x3006
    R49 0x3151
    R50 0x32C3
    R51 0x3300
    R52 0x348C
    R53 0x35B2
    R56 0x3800
    R72 0x4800


    This is the output circuit.

    Thanks!

    Danny

  • 0 in reply to Ryan Seeley
    TI__Genius 12350 points

    Hi Ryan,

    The register configuration and schematic look correct for LVDS (assuming CLKIN of the receiver has an internal 100 Ohm differential termination). When you mention that you don't see an output, are you probing the signal close to the CLKIN pins? Or are you checking the status/output of the receiver? 

    One other thing to try, could you set SWR2PLL = 1 (R72[1]) after loading the config to manually reset the PLL? 

    Regards, 

    Connor 

  • 0 in reply to Connor Lewis
    Prodigy 10 points

    Hi Connor, 

    I am probing at C66 and C67 with an oscilloscope.

    We tried the SW2PLL =1 but still do not see a waveform.

    Regards, 

    Danny

  • 0 in reply to Ryan Seeley
    TI__Genius 12350 points

    Hi Danny, 

    Just to confirm, the device is still responsive on the I2C bus? And is this a brand new device, or has the EEPROM been reprogrammed? 

    Regards, 

    Connor