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DP83867IS: Regarding CLK Input

Darren (FAE)
Expert 5483 points
Part Number: DP83867IS

From Figure 1 of the DS, it looks like XI clock needs to be running before device powers-up, but I can't find a mention of this in the DS.
What kind of timing requirements does the XI clock on power-up/reset?

Consider the following application conditions:
- 2-supply configuration
- XI pin's CLK is 1.8V signal
- In a customer design, VDDA2P5, VDDIO, VDD1P0 are all stable before the CLK is supplied

Is there any issue with the above? (Appreciate any supporting evidence / info if this is acceptable)

Regards,

Darren

  • 0
    TI__Guru**** 190799 points

    Hello Darren, 

    Thank you for the query. Are you using a crystal or oscillator. How is the reset_n being controlled?

    Do you have a snapshot of the schematics that i could quickly review before  answering the query.

    Regards,

    Sreenivasa 

  • 0 in reply to Kallikuppa Sreenivasa
    TI__Expert 5483 points

    Hi Sreenivasa,

    It's 10PM JST so I can't confirm until tomorrow.

    If it was a crystal, the crystal won't start oscillating until device powers up and the XI circuitry drives the crystal, right? In this case, the crystal oscillations happen after power up. What are the requirements on power-up for a crystal?

    If it was an oscillator, there could be a signal applied to the XI input before VDD is applied, like in Fig. 1/2 in the DS.
    So, it shouldn't matter if a voltage is seen at XI before the power rails are up, right?
    But assuming an oscillator, what if the oscillator signal started after device power-up?
    What are the concerns here? Like, does the device need to be in reset until all power rails and CLK are supplied and operating?

    Darren

  • 0 in reply to Darren (FAE)
    TI__Guru**** 190799 points

    Hello Darren, 

    You said it right. the device need to be in reset until all power rails and CLK are supplied and operating.

    Following the power-up and reset timing is what is important.

    Regards,

    Sreenivasa 

  • 0 in reply to Kallikuppa Sreenivasa
    TI__Expert 5483 points

    Hi Sreenivasa,

    Quick final confirmation. Is it fine for an oscillator clock source to be applied to XI before device power-up, as shown in DS Fig. 1/2?
    Current will not flow through ESD diodes, etc...and possibly damage the device?

    Regards,

    Darren

  • 0 in reply to Darren (FAE)
    TI__Guru**** 190799 points

    Hello Darren, 

    Please refer to figure 1 (Power-Up Timing ) and figure 2 (reset timing) in the datasheet and should be fine.

    Regards,

    Sreenivasa