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Clock generator using LM2903-Q1

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Replies: 3

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Dear support Team

We suggest LM2903-Q1 for clock generator.(Prease reffer to attached schematic)

I simulated it and understood that slew rate was an important spec for accuracy.

Could you provide slew rate variation of LM2903-Q1? (rough data is good for us)

Please let me know if there is other recommended IC.

◆Clock generator Spec

Frequency:51.2kHz

Accuracy:±20%  target

Regards

Tomohiro Nagasawa

3 Replies

  • Tomohiro-san,

    I do not think slew rate is the critical factor. I don't have any data on slew rate. Keeping capacitance on Vo node low will help slew rate , rise and fall times.

    Propagation delay will be a more important factor. The characterization data shows a +/-10% variance in 5mV overdrive propagation delay, device to device. Across temperature is a different story. At 125C the delay increases by 63%. At -40C the delay decreases -26%

    The overdrive in this application is time dependent. Increased overdrive lessens prop delay, however the overdrive also increases the peak to peak voltage on the capacitor which reduces frequency compared to the theoretical calculation.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Ron-san

    Thank you for quick response.

    I understand propagation delay is important factor of IC.

    Calcurating the variance of temperature factor only,the variance of propagation delay is +63%/-26% at 5mV overdrive(1.3us typ). 

    The variance of propagation delay @ 5mV is +0.819us(=1.3us×63%)/-0.338us(=1.3us×26%)

    If set frequency to 51.2kHz(≒19.53us), laugh estimate of  frequency is <+8.3%(≒0.819us×2/19.53us)/-3.46%(≒-0.338us×2/19.53us)

    Is it correct?

    Regards

    Tomohiro Nagasawa

  • In reply to Tomohiro Nagasawa:

    Tomohiro-san.

    The effects are hard to calculate. It is best to simulate or build a test circuit.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

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