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LMH6643: LMH6643 capacitor three-point oscillation circuit

Lin_Charles
Expert 4260 points
Part Number: LMH6643

One of our customer use LMH6643MA to build a three-point capacitance oscillation circuit, with ceramic tiles capacitance C, L with coil (used to detect metal);

The question is:

1. Some machines can't afford to vibration or unstable, but when use heater to let LMH6643 hot, it will start up vibration?

2. A part of the machine vibrate normally in the laboratory , but they were vibrating unstable at outdoor, the frequency of signal will jump all thetime? The signal frequency is 80kHz.

Why the frequency is abnormal?

Does the temperature influence the stability of LMH6643, and what can we do to prevent such things happend? 

  • 0
    TI__Genius 15975 points
    Hi Charles,

    To answer your questions:

    1. The LMH6643 are not inherently designed to work as oscillators and they do need certain environment (cold/heating) or supply voltage conditions to start oscillation even if the device is configured in positive feedback.

    2. The variation in signal frequency could probably be coming from the variation in outdoor temperature. Yes, temperature does influence stability of the oscillator.

    In general, I would not recommend using the LMH6643 as an oscillator because of the heating issues involved that could damage the part in terms of long-term reliability of the part. Instead, the customer could look at dedicated low phase noise oscillator chipset for stable 80kHz oscillation frequency. You could probably check with someone in the clock & timing forum to help select an 80kHz oscillator: e2e.ti.com/.../48

    Best Regards,
    Rohit