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Hello,
I have a question about stepping the frequency in 0-Delay mode using TICS-Pro. I am operating it with the following setup:
Device;LMX2581
Evaluation board: LMX2581EVM in original configuration with internal VCO.
Software; Codeloader program version 4.20.02, Part file version 2014-11-09
Reference; 100MHz
Windows 7 SP1 64 bit
Connected with USB2ANY
Register map (for 0-Delay mode):
R15 0x021FE80F
R13 0x4082410D
R10 0x210050CA
R9 0x03C7C039
R8 0x207DDBF8
R7 0x00082317
R6 0x000004C6
R5 0x0030AC05
R4 0x00000004
R3 0x2004F3E3
R2 0x0C000642
R1 0xC2002021
R0 0x700C0000
When I step the frequency using the N divider (PLL_N) from 600MHz to 650MHz in 0 Delay mode in TICS-Pro, I find the output frequency doesn’t step to 650MHz as expected but only to 602.597MHz. I am stepping N from 12 to 13, and have the divider set at 4.
I discovered the only way I can get an accurate step in frequency I need to follow the following procedure:
- Reprogram the synthesiser with saved non 0-Delay mode register map.
- Change the frequency to what I want in non 0-Delay mode.
- Follow the instructions in 8.3.10 in the LMX2581 datasheet to get to 0-Delay mode again.
Are we meant to be able to step it in 0-Delay mode like I first tried? Is there an easier way to get an accurate step? Or is there something I was doing wrong with the software?
Many thanks!
Helen,
With the LMX2581, you can 0-Delay mode, but it is more limited.
You might want to consider the LMX2594 that has a true 0-delay mode that you can step easily likely you want.
Also, consider the LMX2572, which is a lower frequency version of the LMX2594. The LMX2572 is not released, but will be this year and the datasheet is on the web.
Regards,
Dean
Hello Dean,
Thanks for your help! it is much appreciated,
my colleague and I discovered a way that we can get the LMX2581 to do what we want. I thought i'd post it up here incase it is helpful for anyone.
It was discovered that any frequency in between the 50MHz PFD frequency cycle can be obtained by setting the Fpfd frequency smaller (say 1MHz) temporarily. This means you can choose any integer frequency while the Fpfd is 1MHz, and still step it to what is wanted before the VCO becomes uncalibrated. For some reason when the Fpfd is flicked back to 50MHz, the chip stays in O-Delay mode and also fractional mode.
The method used is as below (cumbersome but it works)
Example: Setting to 620.45MHz: (which would be impossible with Fpfd always at 50MHz)
Cheers,
Helen