When i use XTAL input pin the pll can be locked,when use ref pin there is a clock output but no locked signal.
The ref input on the AD9552 is a single-ended 1.8V receiver that's 3.3V tolerant. If you supply an AC-coupled signal, make sure that it's externally DC-biased at 0.9 to 1.0V.
THANKS.I have checked it.The ref input is feeded with a FPGA 3.3V-CMOS output driver.Strangly, i have a dedicated clock out(conf reg),even though 9552 can not locked.
Are you pin-strapping the part, or are you programming the part?
Are both the xtal and ref input present?
Please describe in detail how you're making the part work when using the xtal, and what you change when you switch to the ref input. Bear in mind that switching from the xtal to the ref input requires a reset.
I am programming the part all the time.First i used a xtal(no ref which from a 3.3v cmos fpga output) and then ref input(only ref present).The only change i make just removed the xtal. I did not make a dynamic switch from the xtal to the ref input.Just removed the xtal from the board.When i program the part i do'nt have a locked signal from the LOCKED pin but get a stable clock out.(conf reg refere to the ad9552 edk software)
So just to be clear:
In the case that works, you use an xtal, program the part, cal the VCO, and everything is fine.
Next, you disconnect the xtal, and supply a ref input that is the same frequency, reset the part, and reprogram it, and recalibrate the VCO. Is this correct?
Yes! Is thers anything wrong with my operation? Now, I have the clock output but no LOCDED signal.
What is the value of Register 0x01D?
If the LSB is 1b, set it to 0b.
Used default value 0x00.
Today,i soldered the xtal back,and configed the part as before,it locked.
So i think it's the problem of xtal.if there is a xtal but use ref pin input,it can lock.no xtal,no lock.(no xtal used all the time:just solder the xtal)
use ref alonely no lock,place xtal back it lock.
OK. I'm glad you got it working. To be honest, I'm a bit surprised by the behavior, and will ask the designer for confirmation.
Thanks for you help.I also feel doubt for the behavior,waitting for you good message.
I apologize in advance if I keep asking the same question: If you have the ref input and the xtal connected, are you absolutely sure you're locked to the ref? Can you very the input frequency of the ref input and see a corresponding change in the output frequency?
We have an AD9552 in the lab locked to an external reference without an xtal right now.
Is the xtal input floating? I wonder if the 10 pF load caps on the xtal input are causing a problem.
Maybe there are same other problems.Xtal input floating,Yes.I removed it.If there no xtal soldered the part can not lock(Locked pin).By the way external load cap also removed.
Could please answer a few question for me about your setup?
- What is the frequency of your XTAL?
- What is the frequency of your Reference?
- What are the states of the A[2:0] and Y[5:0] pins? These are pins 5,4,3 and 2,1,32,31,30,29 respectively. If they are left floating, please consider them logic 1 as they all have 100 kohm internal pull up resistors.
- Do you have the ability to vary the frequency of the reference input coming from your FPGA? If so, then please put the AD9552 in the locked state (with XTAL and reference input) and vary the reference input frequency. Observe any changes in the output frequency or locked condition.
- Could you let me know your register programming sequence?
1.XTAL 20MHz(no external load caps soldered)
3.A[2:0],Y[5:0] are left floating.
4.programming sequence :
25MHz ref input
write reg referring to *.stp file
------> write :&H05,&H01(no lock)
FPGA reconfig------> AD9552 reset----->ref pin 50MHz frequency clock input
Just to clarify, the lock status that you are including with your programming sequence is only applicable when both the reference and XTAL are present, but when the XTAL is absent the lock status is always 'no lock', correct? Your register programming sequence is correct and the included locked status is as expected. Your frequency translation is set up such that if the AD9552 where in fact using the XTAL rather than the reference input, it would be operating at an invalid VCO frequency and you would see no lock. So the AD9552 is definitely recognizing the reference input. If everything is identical between your runs except the presence of the XTAL, then I would recommend probing the impedence of the XTAL inputs to ground and supply. This behavior is indicitive of the devices behavior when operating without a XTAL and the XTAL input pins tied to ground or supply. Also try cleaning the PCB around the XTAL pin and pads. Sometimes excess flux left on the board after the soldering/desoldering process will create a short.
Yes.If there only xtal input the part also can be locked(no ref input).
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