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LMX2581EVM: No output and 0V across VbiasVCO with default TICS Pro register values

Jejomar Ildefonso
Genius 9780 points

Part Number: LMX2581EVM
Other Parts Discussed in Thread: LMX2581, USB2ANY

Tool/software:

Hi Team,

Our customer has encountered an issue with their recently purchased LMX2581EVM . Since he's currently unable to post and the board is still within warranty, I'm posting below on his behalf:

Recently I have tried to set up the LMX2581EVM kit and see an output. Firstly, I tested the device with the default values for this device loaded by TICS Pro. 

I have also tested the output frequency through the app to 150,1000MHz, (from 2700MHz default) and there is still no output. 

The current consumption estimate for the default config is 178mA, but there is only ~65mA leaving my power supply. 

The oscillator works as expected. I have tried to debug, and noticed: 

VbiasVCO - 0V
VrefVCO - 1.4v
VbiasCOMP - 2.4V
VregVCO - 2.6V

The VbiasVCO of 0V does not seem right to me. 

Set-up:

The screenshot shows the default values for the PLL+VCO for the LMX2581 loaded by the TI software

0V on the multimeter is across C16, which displays 0V at the VbiasVCO node. I checked the other DC supply voltages at the other nodes in the same way, but the 0V VbiasVCO stood out to me the most as it seems that we are having issues with this part of the circuit.

The waveform on the oscilloscope displays the 100MHz 0.4V oscillator working correctly.

The power supply shows that far less than the expected current is drawn .

I also measured RFout pins using a spectrum analyzer, and don't receive any signal but noise.

Please let me know what you think of this issue and if you need further information. Thanks!

Kind Regards,

Jejomar

  • 0
    TI__Guru** 122540 points

    Hi Jejomar,

    After plugging in USB cable to the USB2ANY, did you get green light in the bottom of TICS Pro? If not, you are not able to program the device on the EVM.

  • 0 in reply to Noel Fung
    TI__Genius 9780 points

    Hi Noel,

    Yes, the green light appears and there is a confirmation for each register after programming with no errors. Unfortunately that screenshot does not show it.

    Kind Regards,

    Jejomar

  • 0 in reply to Jejomar Ildefonso
    TI__Guru** 122540 points

    Hi Jejomar,

    FYI, I've got the following voltage after Vcc power up (without OSCin signal and programming)

    VbiasVCO - 0V
    VrefVCO - 1.56v
    VbiasCOMP - 2.33V
    VregVCO - 2.8V

    current = 34mA (no onboard XO)

    After feeding oscin signal and program (keyboard: CTRL L or  in TISC Pro, USB Communications --> Write All Registers) to lock to EVM default of 2.7GHz,

    VbiasVCO - 1.3V
    VrefVCO - 1.55v
    VbiasCOMP - 2.4V
    VregVCO - 2.78V

    current = 189mA (no onboard XO)

    According to the EVM schematic, the onboard XO is CWX813, which consumes 30mA and output is CMOS. Your data said the voltage swing is only 0.4V, which is too small. I expect you should measure somewhere between 1V and 2V. 

  • 0 in reply to Noel Fung
    TI__Genius 9780 points

    Hi Noel,

    I believe the JTAG cable that the device came with was crimped the wrong way. I didn't suspect this since I received no errors when programming before. I did some exploring and it confirmed that the cable was the case. You can compare the images of the cable that I received in the product package to those of the cable from the USB2ANY user manual and any other picture online. It seems the crimping is wrong by viewing the keys which dictate the direction that it's plugged into the device.

    These attachments show the device with the expected current after reprogramming with the replacement cable. I will test with a spectrum analyzer and oscilloscope tomorrow and flag if anything doesn't behave as expected. However, I am pretty confident that it should work now. VbiasVCO also shows 1.2V after successful program.

    Kind Regards,

    Jejomar

  • +1 in reply to Jejomar Ildefonso
    TI__Guru** 122540 points

    Hi Jejomar,

    Glad that you have another cable to verify and solve the problem.