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LMK00334: No output

Jeff YANG
Genius 5285 points
Part Number: LMK00334

Hi,

I've use LMK00334 but found no output. Would you please help check schematic have anything wrong?

I've meansure some pin condition as below.

VCC  :   3.3V

OSCin : no oscillation

OSCout : no oscillation

CLKout_EN  :  0 V

CLKin_SEL0/ CLKin_SEL1 :  3.3V


Thanks!

Jeff

  • 0
    TI__Genius 11640 points

    Hi Jeff,

    The schematic seems OK to me. Since CLKin_SEL1 is high, the oscillator circuit should have been turned on, so it is strange that it is not doing anything.

    Two questions for now:

    • Are VCCOA and VCCOB also at 3.3V?
    • What is the load capacitance of the crystal?

    I have also paged our buffer expert for additional support.

    Best,

    Evan Su

  • 0 in reply to Evan Su
    TI__Genius 9250 points

    Hi Jeff,

    I think the problem is pull up resistor in this case. I would suggest using a 1 KOhm pull at CLKin_SEL0/1 pin line. Data sheet specifies IIH current of 50uA at 3.3 volt for this input. Based on that you could calculate the maximum pull up resistor value which is 66 KOhm. You need to use a smaller value than that. If you would use 100 K then you would set the pin voltage around 1.3 V which is below VIH threshold value.  This becomes voltage divider at this pin due to internal resistor value that we just calculated.

    You can also use a smaller resistor like 1K for CLKout_EN pin.