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CDCE6214-Q1: PCIe 100MHz default operation

Part Number: CDCE6214-Q1
Other Parts Discussed in Thread: USB2ANY, CDCE6214

Hi,

I have the HW_SW_CTRL pin pulled high on power up and a 25MHz crystal connected. The OE control is also pulled high.  However I'm not getting anything on the outputs.  The supply voltages are nominal at 1.8V.  What should I look for to debug?

Thanks and Regards,

Lee

  • Hi Lee,

    Please first check and see if REFSEL is pulled low. This makes sure that it selects SECREF (XTAL) as reference. If you have I2C connected, read back bit R7[0] LOCK_DET to see if PLL is locked.

    Regards,
    Hao

  • Hi Hao,

    I have REFSEL tied low with 4.7K on the schematic.  I'll verify in the lab tomorrow.

    I will hook up the USB2ANY and work to readback the Lock info.

    Thanks,

    Lee

  • Hi Lee,

    Understood. Please let me know when you have the results.

    Regards,
    Hao

  • Hi Lee,

    I'll temporarily close this thread since it's been open for a few days. You can still reply to it when you have the results.

    Regards,
    Hao 

  • Hi Hao,

    Finally back to this ...  I downloaded the TICSPRO software

    R7[0] = 0 which indicates the PLL is unlocked.

    I noticed my PDN connection is direct to VDD (via a 0 Ohm resistor) without any series resistance. 

    If I probe the 25MHz crystal what amplitude would you expect?

    Anything else I should look for?

    Thanks and Regards,

    Lee 

  • Hi Lee,

    The voltage amplitude of the crystal cannot be predicted and we typically measure the current flowing through the crystal. For details, please look at this appnote: https://www.ti.com/lit/an/snaa331/snaa331.pdf?ts=1595820920482&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FCDCE6214-Q1

    Regardless, the PDN pin cannot be tied to VDD directly. You can use external 4.7k pull up and 0.47uF cap to ground in order to slow down the PDN pin ramping. Alternatively, just float PDN pin because it has 50kOhm internal pullup.

    Regards,
    Hao

  • Thanks Hao.  Will update the PDN connection and see if that allows the part to start up.

    Regards,

    Lee

  • No problem. Let me know.

    Regards,
    Hao

  • Hi Hao,

    Adding a capacitor to GND is not changing the CDCE6214 power up response.  Is there something I can do to reload or program settings for 100MHz outputs?

    Thanks,

    Lee

  • Hi Lee,

    Did you also remove or replace the 0Ohm resistor between VDD and PDN pin? 

    Yes you can use Ticspro to program the device. You can start with default configurations (in the tool bar) for sanity check.

    Regards,
    Hao

  • Hi Hao,

    I removed the 0 Ohm and added a 0.1uF to GND to end up with a RC on the PDN pin.  I'll be working on this later today.

    Regards,

    Lee

  • OK. Let me know when you have the results.

    Regards,
    Hao

  • Hi Hao,

    I removed the 0 Ohm to VDD resistor. Now there is only the internal pullup and an external 0.1uF to GND

    I can see on a scope that the XTAL input is receiving 25 MHz. 

    In the TICS software I can enable the REFCLK output and see 25 MHz.  I can also see the PLL is showing "Locked", but I can not seem to make the other outputs work. When I change OUT0 between REFCLK and PFD I expected the frequency to double, but it stays at 25 MHz.  If I select REFCLK as the input to the other outputs they still do not output a signal.  I expected to see a 25 MHz/6 output frequency.

    Hope this information helps to move the debug forward,

    Regards,

    Lee

  • Hi Lee,

    If you load one of the default configurations (in the tool bar, from Default Configuration, select the second one for example), do you see normal behaviors?

    Regards,
    Hao

  • Hi Hao,

    If I click on the default setting in TICS Pro the outputs will all start up at 100MHz.

    The output voltage seems a little on the low side just about 0 - 300mV.  I used a 33 ohm - 50 ohm resistor combination on the outputs.

    Additional questions.

    I have a 25 MHz XTAL with 8p load.  Should I adjust the drive to match this value?

    Here is my schematic - still not having any success to have these outputs turn "on" at power up.

    Regards,

    Lee

    Thanks,

    Lee

  • Hi Lee,

    In the default EEPROM page 1, GPIO1 is configured as OE, so it needs to be pulled high or left floating for all outputs to be enabled. In your schematic, however, this pin is labeled as SSC_EN. Can you double check the state of this pin?

    The HCSL outputs do not need any external termination. There's internal 50Ohm to ground and that's all the termination that's needed. Also you need to use high impedance Oscope termination to avoid double termination and halving the swing.

    The internal load capacitance can be adjusted here: 

    Load cap impacts the frequency accuracy. You can increase the load cap to decrement output frequency or reduce load cap to increment output frequency. This is the differential load cap. It doesn't mean that this value should be set to 8 because there's also PCB stray capacitance. You can start with ~5.5pF and measure output frequency using a frequency counter.

    Attached is the page 1 EEPROM configuration: 

    CDCE6214-Q1 EEPROM page 1.txt
    R85	0x00550000
    R84	0x00540000
    R83	0x0053FF00
    R82	0x005201C0
    R81	0x00510004
    R80	0x00500008
    R79	0x004F0008
    R78	0x004E0000
    R77	0x004D0002
    R76	0x004C0188
    R75	0x004B8008
    R74	0x004AA181
    R73	0x00490000
    R72	0x00480006
    R71	0x00470406
    R70	0x00460808
    R69	0x0045A181
    R68	0x00440000
    R67	0x00430006
    R66	0x00420006
    R65	0x00414808
    R64	0x0040A181
    R63	0x003F0000
    R62	0x003E0006
    R61	0x003D0000
    R60	0x003C6028
    R59	0x003B8008
    R58	0x003A502C
    R57	0x00390000
    R56	0x00380006
    R55	0x0037001E
    R54	0x00363400
    R53	0x00350069
    R52	0x00345000
    R51	0x003340C0
    R50	0x003201C0
    R49	0x00310013
    R48	0x00301A05
    R47	0x002F0280
    R46	0x002E0000
    R45	0x002D4F80
    R44	0x002C0318
    R43	0x002B0051
    R42	0x002A0002
    R41	0x00290000
    R40	0x00280000
    R39	0x00270000
    R38	0x00260000
    R37	0x00250000
    R36	0x00240000
    R35	0x00230028
    R34	0x00220000
    R33	0x00210000
    R32	0x00200000
    R31	0x001F0000
    R30	0x001E0030
    R29	0x001D0000
    R28	0x001C0000
    R27	0x001B0004
    R26	0x001A0000
    R25	0x00190400
    R24	0x0018091C
    R23	0x00172406
    R22	0x001606A2
    R21	0x00150513
    R20	0x00140000
    R19	0x00130000
    R18	0x00120000
    R17	0x001126C4
    R16	0x0010921F
    R15	0x000FA037
    R14	0x000E0000
    R13	0x000D0000
    R12	0x000C7002
    R11	0x000B003F
    R10	0x000AA777
    R9	0x0009A777
    R8	0x00080001
    R7	0x00070C0D
    R6	0x00060E6C
    R5	0x00050008
    R4	0x00040000
    R3	0x00030200
    R2	0x00020000
    R1	0x00017652
    R0	0x00002000
    

    You can see if things work after manually loading this config. If it works, then it might mean that the factory default EEPROM has been corrupted. You can overwrite the EEPROM for sanity check. The EERPOM can be overwritten in the EEPROM page of Ticspro.

    Regards,
    Hao

  • Hi Hao,

    Thanks for the help.  This has fixed my startup issue.  I quickly removed the external 50 Ohm pulldowns and this helped the amplitude.  I will replace my series resistors with 0 Ohm values to improve my waveform shape.

    I will work through the rest of the configuration to see if I need to write custom EEPROM pages or just leave the default.

    Thanks and Regards,

    Lee