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IWR1843: IWR1843 external clock

c64
Intellectual 480 points
Part Number: IWR1843

Hi,

I'm considering a design with an external clock for an IWR1843 sensor, and since I need it to withstand high-g shocks and be very small, I can't use just any clock. I had in mind the SiT8918 MEMS clock (www.sitime.com/.../sit8918), but it has a full output swing equal to Vdd, meaning minimum 1.8 V. From what I can see from the IWR1843 datasheet, the external clock AC amplitude must be within 700 and 1200 mV. Is there any way I could use the SiT8918 MEMS clock as an external clock to IWR1843?

Thanks!

  • 0
    TI__Mastermind 25835 points

    Hello,

         You could use external clock, care need to be taken to meet the phase noise spec as provided in the Datasheet.

    Also while using external clock CLKM pin need to be grounded and single ended clock is applied to CLKP pin through AC coupled option. You may use capacitor divider to bring the voltage swing acceptable levels at the input of CLKP pin. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    Intellectual 480 points

    Hi,

    Thank you for your response. Just a question, you mention that "single ended clock is applied to CLKP pin through AC coupled option". Now, the output of the SiT8918 MEMS device is a square wave from GND to Vdd, where Vdd can be 1.8 V, or between 2.5 and 3.3 V. Why should this be AC coupled? And how would you suggest using a capacitor divider in this application?

    Thanks!

  • 0 in reply to c64
    TI__Mastermind 25835 points

    Hello,

        If the input is AC sinewave then AC coupled configuration is recommended. If the input is square wave DC coupled configuration could be used. To reduce the swing resistor divider network could be used, But resistor divider adds noise, hence capacitor based divider could be use at the output of the oscillator before connecting input of the CLKP pin. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.