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Posts: 4
Registered: ‎07-24-2015
Accepted Solution

How to test automatic clock switching on Si5344?

Hi,
We are testing input clock switching in Si5344. We have replaced the Si5340 in the Si5340-EVB. The PCB is identical for both ICs and it work.

 

We configured input reference as manual and IN0 as input reference (10MHz LVCMOS). It come from spectrum analyser HP6369E 10MHz reference output.


We executed the following tests (using ClockBuilder Pro v2.2):

 

Test 1:
Set Input Clock in Manual Mode,
Register = IN0. Write bytes (CLK_SWITCH_MODE, IN_SEL_REGCTRL, IN_SEL) using Si538x,4x EVB GUI.
IN0 = Reference 10MHz.
Result: If we disconnect the reference IN0 the output OUT0 (100MHz) still working. Why it still working if no reference is connected? it is forced to be only IN0.

 

Test 2:
Set Input Clock in Manual Mode,
Pins = IN0. (jumpers in PCB configured to use IN0, JP3 and JP4 set)
IN0 = Reference 10MHz from spectrum analyser HP6369E.
Result: Same result Test 1, but forced by hardware, same question.

 

Test 3:
Set Input Clock in Automatic Mode,
IN0 = Reference 100MHz from signal generator RS SML01.
Result: We change frequency in signal generator, and no change is observed in OUT0.

 

Test 4:
Set External Reference Source (step 3/15) to XO. This is because the EVB PCB have Xtal. We want to disable internal reference (Xtal) and use External reference from IN0.
Set Input Clock in Manual Mode,
Pins = IN0. (jumpers in PCB configured to use IN0, JP3 and JP4 set)
IN0 = Reference 10MHz from spectrum analyser HP6369E.
Result: No signal at OUT0. Why there is no signal at OUT0?, we have external signal at IN0. It is necessary to have clock signal in Xa/Xb to work?

Test 5:
Set External Reference Source (step 3/15) to XO. Because the EVB PCB have Xtal, configuring the IC to use XO produce no signal on OUT0.
Set Input Clock in Automatic Mode,
IN0 = Reference 10MHz from spectrum analyser HP6369E.
Result: The same for test 4.

 

We think Automatic switching is not working and IC still using internal reference (Xtal in PCB XA/XB input). What we are doing wrong? How we could test automatic clock switching?

 

Thank you.

 

Posts: 4
Registered: ‎07-24-2015

Re: How to test automatic clock switching on Si5344? (SOLVED)

Hello,

We found an error in IC configuration (in ClockBuilder).

Since we have 2 different input references with different frequencies; 100MHz (IN1) and 10MHz (IN0), we need to uncheck Precision OOF and Fast OOF in step 15 (ClockBuilder). (Section 5.7.3.1. Precision OOF Monitor pdf datasheet).

This feature is when you need to check frequency deviations on references with same frequency. It is not our case.

 

Best regards.

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Posts: 63
Registered: ‎09-10-2014

Re: How to test automatic clock switching on Si5344? (SOLVED)

Hi,

 

Your useage of the Si5344 is wrong.

 

The Si5342/44/45 are jitter attenuators.

 

This means:

 

1. They need a crystal reference (reference for jitter cleaning. Never disable this and please enable crystal mode on the EVB and in your system).

2. They will filter jitter on any input (like the input IN0 = 10 MHz, continue to use the input at IN0).

3. When IN0 disappears, the part is designed to "holdover" i.e. hold output the same until the input is back.

4. When you have multiple inputs , say IN0, IN1 and IN0 disappears, the part can "AUTOMATICALLY SWITCH TO IN1" but if you "dynamically change IN0, it is programmed to go to holdover as in #3.

 

So, what you have observed in Test 1 and 2 is correct.

 

Test 3 is wrong usage of the part. This part has a limited PLL range and therefore, its ability to track large dynamic changes in clock frequency (greater than 500 ppm) is NOT POSSIBLE.

 

Test 4 and 5 are also wrong usage. They violate condition #1 above.

 

If you need a wide-band PLL, please use Si5340/41.

 

Also, can you please send an e-mail to harihara.Subramanian@silabs.com (myself) with the application you are trying to realize. I might be able to support you appropriately.

 

Regards,

Hari