LMX2594: Unexpected R110 Readback

Daniel Perkins

Part Number: LMX2594

Tool/software:

After programming, I read R110 to determine lock status. The readback value is 0x0708. This suggests that the PLL is unlocked, has an invalid VCO select and has fixed bits that do not match the data sheet. I have verified that the output clock is what I expect, and when I set the MUXOUT_LD_SEL bit to '1', it shows me that the PLL is locked. So, I think it's getting programmed correctly but my readback of R110 is invalid. However, I CAN readback other registers correctly and have verified via scoping that the SPI bus waveforms are good. Any known issues with this?

5 months ago

0 Noel Fung 5 months ago

TI__Guru** 108410 points

Hi Daniel,

What is your LD_TYPE setting? If the value is 0x0, rb_LD_VTUNE is not going to work. You need to set LD_TYPE = 0x1, do a VCO calibration and then read back R110.

0 Daniel Perkins 5 months ago in reply to Noel Fung

Prodigy 10 points

Noel,

Thank you, LD_TYPE was, indeed, set to 0. I tried programming with it set to 1 and am running VCO calibration. I am now getting an R110 readback of 0x00EA which appears to still be invalid. I am expecting all fixed bits in R110 to be zero.

0 Noel Fung 5 months ago in reply to Daniel Perkins

TI__Guru** 108410 points

Hi Daniel,

R110 is a read only register, please focus on the two specified fields, for the other bits, you may read back different value than 0.

anyway, you still read back 0x0 for rb_LD_VTUNE, this is not correct. Can you confirm the Vtune voltage is apporx. 1.3V? rb_VCO_SEL shown you are using VCO7, what is the VCO frequency you are locking to?

0 Daniel Perkins 5 months ago in reply to Noel Fung

Prodigy 10 points

I am now reading back 0x06EA. Not sure why rb_LD_VTUNE was 0 before. My Vtune voltage depends on how I set the charge pump gain in TicsPro. When set to 0mA, Vtune is ~170mV. Sounds like I have a loop filter problem. VCO frequency in TicsPro is set to 11796.48 MHz.

0 Daniel Perkins 5 months ago in reply to Daniel Perkins

Prodigy 10 points

LMXPLLADC.tcs

Here is my ticspro file

0 Noel Fung 5 months ago in reply to Daniel Perkins

TI__Guru** 108410 points

Hi Daniel,

0mA = tri-state, the loop is open, that's why it is unlock.

If you are using the EVM's loop filter, set the current to 15mA.

This frequency should be taken care with VCO4.

0 Daniel Perkins 5 months ago in reply to Noel Fung

Prodigy 10 points

OK, thanks. I'll try some variations. I have tried other charge pump settings, including 15mA. For those, I was getting lower Vtune voltages. I'm not using the EVM. This is a custom board. I'm not the designer, but I can engage that party.

Clock & timing

Clock & timing forum

LMX2594: Unexpected R110 Readback