Tlc04 anyone used it?

Discussion in 'Analog & Mixed-Signal Design' started by geoffers, Aug 3, 2016.

  1. geoffers

    Thread Starter Active Member

    Oct 25, 2010
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    6
    Hi all,
    I'm playing around with a tlc04 low pass filter chip at the moment, just wonder if any one here has used one?
    I have it working , the one I have sets the cut off at 1/50 of the input clock, which at the moment is a rc (it can be TTL or CMOS ), in the datasheet it says that over 250khz should be 50%duty cycle, can I assume my rc to be around 50% or did I ought drive it from a pic pin? My input frequency is 500 ish kHz
    Thanks Geoff
     
  2. #12

    Expert

    Nov 30, 2010
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    According to the datasheet, the input threshold voltage has a very wide range, like 40% variation is possible. This is bad. Check with a 'scope, but the specifications are rather bad.
     
  3. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Thanks for the swift reply ,
    I see what you mean, looking at it would I get better results driving it with a pwm from a pic, if the rise and fall of the pin are fast it should give a more accurate cut off point? Or should I look at a different part? It is cheap :)
     
  4. #12

    Expert

    Nov 30, 2010
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    I don't know squat about other filter chips, I just know how to be really picky about specifications.
    The Schmidt trigger and the follower amplifier take care of, "fast" transitions but they are miserable for duty cycle.
    I suggest you forget the RC method and use something else for a clock.
    However, the definition of PWM is, "not a 50% duty cycle". If PWM was always a 50% duty cycle, all the widths would be the same, thus, no modulation.
    Sit down and think for a minute. You need an oscillator with 50% duty cycle, and it's not width modulated.
    You can probably do that with a PIC.
     
    geoffers likes this.
  5. geoffers

    Thread Starter Active Member

    Oct 25, 2010
    239
    6
    Thanks, sorry for lazy definitions , I have a 'spare' pwm module on the pic I could use to drive the filter, set it going and I can kind of forget about from a code point of view.
    Cheers for looking at it , Geoff
     
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