CDCM6208V1F: The PLL of CDCM6208 can't locked

RAY TOMS

Part Number: CDCM6208V1F
Other Parts Discussed in Thread: CDCM6208, CDCM6208V1EVM

Hi all , I have a question about CDCM6208.I have a development board with CDCM6208.I configurate the CDCM6208 with SPI mode but it can't work and PLL of it isn't locked.Why for it?

The Phenomenon of it is followed :

1.SPI is normal because I can write register and read the correct value of it.

2.I set register3 0x10F0 while the pin of status1 is high and status0 is low.

3. I measure the voltage of ELF pin and the voltage is almost zero (0.015V).

4.The output pins of CDCM6208 have no clock.

The follow picture is schematic of my board:

PS: the power supply of CDCM6208 is VDD_PLL1(3.3V),VDD_PLL2(3.3V),CDCM_DVDD(2.5V)

The following picture is my SPI configuration:

I also have an extra question:

1. Whether the power supply of VDD_SEC_REF must be equal with VDD_VCO?

I hope to get a reply soon. Thanks!

over 6 years ago

0 Vibhu Vanjari over 6 years ago

TI__Genius 11900 points

Hello Ray,

I am looking into this. Just to summarize you have a 25MHz crystal on SECREF that is detected but the PLL but does not lock.

0 Vibhu Vanjari over 6 years ago

TI__Genius 11900 points

Hello Ray,

I took your register settings and loaded them on to the CDCM6208V1EVM. I did not have any trouble with the PLL locking.

Here are some things to try:

1) Click on the Calibrate button to re-calibrate the PLL.

2) Probe your SEC_REF input to ensure there is an input clock.

The datasheet states that the VDD_VCO and the VDD_PLL2 supply pins can be combined as they are both analog and sensitive supplies. This is a recommendation to avoid high power supply noise.

A note on your schematic, refer to the EVM User's Guide Figure 7. for an example of supply (VDD_X) pin filtering/bypassing.

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CDCM6208V1F: The PLL of CDCM6208 can't locked