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TINA/Spice/TLC552: TLC552

Aart Nagelhout
Prodigy 40 points
Part Number: TLC552
Other Parts Discussed in Thread: TINA-TI, , TLC556, SN74LVC1G123

Tool/software: TINA-TI or Spice Models

I'm trying to simulate with part TLC556 and TLC552.
When I'm calculating the results myself with the provided formula's from the datasheet the results don't match.

I'm using the astable configuration


For example when simulating model TLC556 with the default provided values
Ra=2890Ohm
Rb= 11540Ohm
C1 =10nF

The title of the model states this should result in 10kHz
but when simulating I see ~8.5Khz (after removing the diode)
and when calculating the results using the datasheets formuals I get 5.55khz

Why do the results differ so much?

I'd like to use the TLC 552 (low supply voltage) in an ATE setup.

appreciate your feedback,

Kind regards,
Aart Nagelhout

  • 0
    TI__Guru*** 149776 points
    Aart,

    Can you attach the TI-Tina schematic.tsc file to a reply?
  • 0 in reply to Ron Michallick
    Prodigy 40 points

    Hi Ron,

    I inserted the model I used as reference.

    I actually want to use the TLC552 as this is a low voltage dual channel timer, but the datasheet of this model doesn't have any formula's (I assume formulas are the same for all these devices?...).

    My idea is to vary the capacitance, C1 between 75pF and 270pF (it's a capacitance bank controlled by digital logic)

    I'd like to have the frequency as high as possible to get the highest accuracy, so for the TLC552 up to 2.1Mhz.

    The voltage at the capacitor C1 may not be above 1.8V, so that's another restriction at the supply side.

    Hope you can help me out with this one

    Kind regards,

    Aart Nagelhout

    slfm008.tsc

  • 0 in reply to Aart Nagelhout
    TI__Guru*** 149776 points
    Aart,

    I also removed the diode and the period became 184us which is 5.43 kHz.
    1.44 / [(2.89k + 2* 11.54k ) * 10nF ] = 5.54 kHz

    I would expect that running at 10% of maximum frequency (200kHz) would be more accurate as the propagation delay would affect the output frequency less.
  • 0 in reply to Ron Michallick
    Prodigy 40 points
    Hi Ronald,

    Thanks for your reply.

    OK at these lower frequencies it seems to work as expected.
    However, at higher frequencies the formula doesn't match the simulation anymore.

    I'd like to have the frequency as high as possible (2.1Mhz ) when connecting 75pF what resistor values do you suggest then?
    Supply voltage at 1.8V.

    Kind regards,
    Aart Nagelhout
  • 0 in reply to Aart Nagelhout
    TI__Guru*** 149776 points

    Aart,

    I do not recommend TLC552 if both 2MHz and frequency accuracy is needed.
    I suggest the SN74LVC1G123 logic timer that has a low minimum VCC and a high maximum frequency.