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Clocks & Timers
Clocks & Timers Forum
CDCE62005 practical questions about EEPROM, Loop filter and other things
Here a Q&A that might be helpful to others:
1) Can the CDCE62005 be purchased preprogrammed to a setting of our choosing?
Yes, through Avnet, who is setup to do this programing for this device. 5) On my design I will not use the secondary input port, what does TI prescribe for tying this unused port off?
You can disable this input and tie it to GND through a pull-down of a few kΩ on each input leg.
7) Why does TI recommend Y5V vs X7R caps on pins 4 & 38.
The capacitors need to have a particular ESR. I assume we are looking for a low ESR for the internal regulator.
8) What is the range of loopbandwidth (low to high) that I can set the filter to while running at 500MHz with a 25MHz xtal on the aux. note: my study shows that the range is a function of settings and that the range with my settings ~65kHz=>1GHz.
Loop bandwidth ranges from 30Hz up to fPFD/10, but you should not aim for anything higher than 500kHz. For a 25MHz XTAL, I would recommend aiming for 300kHz (maybe also try 400kHz, as you can all these values by simply using the internal loop filter and reconfiguring).
9) How shall I go about choosing the optimal setting? There are many?
Target the following:
Phase Margin= aim for 60-70 (65 is great)
Gamma= make it at least one, 10 is best, make it less than 100 I’d say
R3: minimize (e.g. 5k)
C3: set it such that 3rd pole is at least 10x higher than BW (e.g. 3MHz); If in doubt, minimize C3
C1: don’t use less than 10pF
C2: I would use max value at 473.5pF
R2: set it such that you get the right BW, likely 4k or 9k
ICP: make it at least 300uA, I would aim for 600uA if possible with the combinations of the other components.
Here is a setting that would be really good:
10) Is the GUI setup software stable?
11) Can I run the TI setup software with another host adaptor (someone elses spi port tool)?
Not easily, because the GUI tries to access a particular driver inside the USB receiver and there is no documentation how to do this.
12) Can TI recommend a SPI tool?
We do have stand-alone USB dongles that can convert USB into SPI and use the driver from our EVM I believe.
Most customers write their own SPI sequence with a controller.
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