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Original question:

SN65HVD63: SN65HVD62 application circuit-crystal

SN65HVD63: crystal drive power level

Zach Xia
Expert 6795 points
Part Number: SN65HVD63
Other Parts Discussed in Thread: LMK6C,

Hi expert,

How much drive power would be forced on the crystal if connected with this device? Since the crystal has a drive level limit 300uW like below. Thanks!

  • 0
    TI__Mastermind 46807 points

    Hi Zach,

    This can be found by looking at two specs:

    1. VIH/VIL - this is spec'd for the XTAL pins as a max of VCC for VIH and a max of 30%VCC for VIL - so worst case scenario is VCC (which can be 3V - 5.5V) 

    2. Leakage Current on XTAL pins when voltage is between 0V and VCC is +/-15uA.

    So with those specs worst case power on one XTAL pin is VCC * 15u = 65uW (VCC - 5V) or 45uW for VCC=3V. Both pins shouldn't be maxing out at the same time however so while both pins could be burning power it shouldn't exceed 110 uW- 120uW if using under datasheet recommended conditions. So I think using this crystal should be okay because in most applications you probably won't be getting the max leakage (+/-15uA) so power will probably be lower in most situations. But there shouldn't be a concern of exceeding the ratings of the crystal you have given.

    Please let me know if you have any more questions!

    Best,

    Parker Dodson 

  • 0 in reply to Parker Dodson
    TI__Expert 6795 points

    Hi Parker,

    Do you think LMK6C fit for this? Thanks!

  • 0 in reply to Zach Xia
    TI__Mastermind 46807 points

    Hi Zach,

    I don't think so - the oscillation frequency for the LMK6C seems to be much too fast for this device (minimum seems to be 200MHz and this device is looking for an input reference of 8.704MHz). So while the LMK6C does seem to be a high performance part it doesn't seem to match this application. This part is designed for a crystal oscillator or oscillation circuit that can hit that reference. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    TI__Expert 6795 points

    The freq range of LMK6C should be 1-200MHz. So could you help check other parameter could meet?

  • 0 in reply to Zach Xia
    TI__Mastermind 46807 points

    Yes - I see that know I apologize.

    I am looping in the product line responsible for this part as they will have more in-depth information than me- to answer further questions. I don't think this part requires something this high grade and a normal crystal is what this part this part is designed for. 

    Best,

    Parker  Dodson

  • 0 in reply to Parker Dodson
    TI__Expert 6795 points

    Hi Parker,

    My customer said they cannot get a XTAL with 8.704MHz from supplier. So we are discussing if a clock signal is good for SN65HVD63. And what's the requirement of the clk signal, LVCOMS? How much jitter?

  • 0 in reply to Parker Dodson
    TI__Mastermind 20900 points

    Hi Zach,

    i agree with Parker, that the LMK6C might be too high performance. You can likely use an XO like the LMK6C to drive the XTAL1 pin instead of a Xtal.

    But an Xtal is probably the best solution here.

    regards,

    Julian