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TLV1805: Design procedure to use as an Oscillator

Siddhesh Rahula
Prodigy 40 points
Part Number: TLV1805

Dear TI Team,

We are planning to use TLV1805 as an oscillator (in the MHz range). TLVs' datasheet does not contain a design procedure to use TLV as an oscillator.

The link from its datasheet leading to an oscillator design (Engineers Cookbook Circuit entitled Oscillator Circuit (SNOA990))" is not active anymore. (https://www.ti.com/lit/pdf/SNOA990)

Can you please provide me the design procedure to use TLV1805 as an oscillator?

Best regards,

Siddhesh

  • 0
    TI__Mastermind 49896 points

    Hello Siddhesh,

    SNOA990 seems to have been pulled from the web. I will look into that.

    Another oscillator application note is SNOA998. Basically the same:

    Relaxation oscillator circuit

    The MHz range may be stretching it for the TLV1805 - depending on the supply voltage and actual frequency. Output loading will have a great effect of the actual frequency. Why did you pick the TLV1805?

    You may be better off using a simple logic gate RC oscillator to generate the frequency. That may be more stable and easier to control.

  • 0
    Guru 140200 points

    Hi Sidesh,

    today, I would go for a ready made quarz oscillator chip. They are tiny, cheap, uncomplicated, stable and draw very small supply current compared to earlier oscillators. In my eyes they are just unbeatable.

    Kai

  • 0
    TI__Mastermind 49896 points

    Hello Siddhesh,

    It seems appnote SNOA998 was released in favor of SNOA990, but the TLV1805 datasheet was released before that decision was made, so it needs to be corrected.

    The two appnotes are basically the same - same schematic and same formulas, just a little different formatting. So use SNOA998.

    If you do choose to use the TLV1805 as the MHz oscillator, the C values start getting small, and the effects of parasitics and device variations (including loads) start to cause variations in the frequency.

    As Kai and I both recommend, a separate oscillator is recommended for higher frequencies.

    Also keep in mind that the theoretical toggle frequency for the TLV1805 is around 1.5MHz...and even then the output may be starting to get distorted.

    If you are driving a large capacitive load (>1nF), you may start getting into power dissipation limits quickly charging/discharging capacitive loads at these frequencies.