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LM567C

Mike Batten
Prodigy 40 points
Other Parts Discussed in Thread: LM567C, LMC567

Looking for best values R1, C1, C2 to use for a 40KHz tone decoder with the widest possible reliable BW for this part.

I have experimented with R1 (24K), C1 (.001Uf) and C2 (.01uf) but my real results do not mimic my calculations

 

  • 0
    TI__Guru**** 189401 points

    Hi, Mike,

    Sorry for the delay. I've asked my colleague Jeff to look into this for you.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 40 points

    Don,

    Thank you but I think I have figured out what I needed.  The spec sheet is very poor to not include this information unless I missed it somewhere but nothing I found directed me to this so I experimented to figure out the cycles needed before producing an output in the tone decoder circuit.

     

    I used a 27K (R1) and .001uf (C1) to set up the 40KHz Fc and selected .02 (C2)  for the bandwidth  even though it calculated larger than the typical bandwidth % for the given Fc.

     

    My next problem was wanting to wait for 3 to 4 cycles of 40KHz before the output would trigger and no matter how I changed the values, it would always trigger after 1 cycle.

     

    My new issue is that I have tried the LM567 from different date codes with the same R1 and C1 values and I am seeing  a change in Fc of several KHz.  Is this normal? I was hoping to not need an adjustable value here as I was shooting for an 8KHz bandwidth but even with the 8Khz bandwidth I am finding that some lots require I chance R1 to 24K in order to detect the 40Khz tone.

     

    Any advise would be appreciated.

     

    It was not until I experimented with the capacitor on Pin 1 that I was able to get it to wait for 2 cycles, then 3 cycles, then 4 cycles depending on the C value I installed for C3.

     

     

  • 0 in reply to Mike Batten
    TI__Prodigy 385 points

    Hello,

    Sorry for the delay, I have been out of town.  Let me take a look and I will get you some more info.

    Jeff,

  • 0 in reply to Jeffrey Bridges
    TI__Prodigy 385 points

    Hi Mike,

    I am getting about the same results as you.  The center frequency is running higher than the equations in the datasheet suggest.  However, you could try a couple other things.  The post references the LM567C grade part.  The LM567 (non-C) grade part has tigher specifications and should give better results.  The LMC567 is pin-pin compatible with some slight differences in specs.  The main point being that the LMC567 has an accuracy specification (about +/-10% not including component variation) where the LM567/C do not.  That may get you to the point where you do not need to trim.

     

    Best Regards,

    Jeff

  • 0 in reply to Jeffrey Bridges
    Prodigy 40 points

    Yes, I have some that run higher and some that run lower, yes I am currently using the LM567C.

     

    I did not see where the C was that much worse than the non C in the spec that would have equated to +/-10% but clearly I am having issues that don't jive with the calculated results so I guess it is what it is.  Even the bandwidth is all over the place with some having 15Khz and some having 4Khz and the rest somewhere in between all with the same values.

    I can try the LM567 but I will need to sample a few from several different lots to have more confidence in its repeatability.  I would prefer not to set up an adjustment for this as it will then require a procedure for checking the bandwidth and setting the adjustment for a 40khz midpoint in a production environment.

     

     

  • 0 in reply to Mike Batten
    TI__Prodigy 385 points

    Hi Mike,

    I wanted to make sure we are referring to the correct parts:

     

    1)  LM567 & LM567C are on the same datasheet and are bipolar parts.

    2)  LMC567 is a newer version and is an LMCMOS part.  This one has the accuracy guarantee.

     

    Jeff,

  • 0 in reply to Jeffrey Bridges
    Prodigy 40 points

    I was not aware of the newer LMC567 ad it improved accuracy.  I will review the specs.  Thank you