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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Tekelec on November 14, 2022, 12:06:42 pm

Title: Connecting a cmos oscillator to chip
Post by: Tekelec on November 14, 2022, 12:06:42 pm

Hi
I have a cmos 12mhz oscillator part number LFSPXO020465 which I'm using as an external clock for a DAC project.

I'm having an issue where unless I install a series resistor between the oscillator output and the DAC chip (ms8416t) then after a few hours it kills the DAC. I have scoped the oscillator voltage and is around 90% a vcc at peak as expected. Installing the resistor saves the chip but also affects the wave form, that is it changes from a square wave to a triangle.

My question is should the oscillator be coupled via a capacitor or a resistor to the IC?
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Title: Re: Connecting a cmos oscillator to chip
Post by: Zero999 on November 16, 2022, 05:11:03 pm

It's possible for reflections in an unmatched line to cause higher voltage spikes.

How close is the oscillator to the chip? Did you measure the actual voltage going to the chip? Bear in mind the oscilloscope probe can load it down.

What value resistor did you use? Which end was the resistor connected? You could try a 100R resistor in series with 47pF, between the clock and 0V, right next to the chip, to provide a load for the higher frequency elements of the signal.