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CDCM6208 input (crystal mode)

Xuezhuan
Prodigy 100 points
Other Parts Discussed in Thread: CDCM6208

Hi Expert,

The pin mode is used, and we use the following configuration, the secondary input is crystal according to the configuration.

Can we directly connect a single ended clock (3.3V CMOS/TTL) to the secondary input pins? how to connect it? thanks.

  • 0
    TI__Expert 4400 points

    It is not recommended to connect a single ended input to SEC_REF. Can you get the swing down to a 1V swing on the PRI_REF. This way, you connect the signal to P and then tie N to a 500 ohm to the common mode voltage (between 0.8V and 1.5V).

  • 0 in reply to Madhu Balasubramanian
    Prodigy 100 points

    Hi Madhu,

    You mean we can use your method to connect single ended input to LVDS PRI_REF input and keep current PIN mode?

    another question is, in PIN mode, when PDN pin is LOW, if all of the internal blocks will power down include crystal circuits?

  • 0 in reply to Xuezhuan
    TI__Expert 4400 points

    Hi Xuezhuan,

    My method works only if Vcc on CDCM6208 is 2.5V or 1.8V. In this case, Figure 19 of datasheet can be used to connect PRI_REF_P to reduced LVCMOS signal (to below 1V) and then you connect PRI_REF_N to only the termination resistors as shown in Figure 19.

    If supply to CDCM6208 is 3.3V, my recommendation will not work and there is no solution unless you provide LVDS signal to the primary input.

    Also when PDN pin is low, then all internal blocks including crystal circuits will be powered down.