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TLC393 / output voltage at low VDD

Other Parts Discussed in Thread: TLC393, TLV1702, TLC352, TLC339, TLC372, TLC3702


We are considering  output voltage is unexpected when low VDD.

The output voltage should be low on this condition.

What is the VDD voltage to change output voltage high to low as expected ?

Best Regards,


  • What is 'low Vdd'? The part operates from 3V to 4V depending on the suffix.

    The part should work even though you are violating the input common mode range on the inverting input; it may not be as fast as spec'ed.

    However, if you are at lower Voltages than 3 or 4 then something may be getting crushed, probably the input stage. 


  • Hello Kato-san,

    Tying the TLC393 inverting input directly to VDD violates the positive input common-mode input range, VICR. The VICR limit is VDD - 1 V at 25 C, and VDD - 1.5 V, 0 to 70 C. If the VICR limit is exceeded the output may not be at the expected level, or in the expected state.

    If the TLC393 VICR range is observed, then the output state should be in conformance with the comparator expected behavior. Regarding the low-level output voltage level VOL, TLC393 data sheet Typical Characteristics figure 8 graph provides the pull-down voltage information based on VDD and the (sink) output current .

    If the application requires a rail-to-rail VICR range, you may want to consider a more modern comparator such as the TLV1702. The data sheet can be viewed here:

    Regards, Thomas

    PA - Linear Applications Engineering

  • Hello Thomas,

    Is the VICMR behavior specific to the TLC393? I know most comparators that I have used will operate correctly as long as *one* input is in the common mode range. Delay time may not be in spec, but it will work.


  • Hello Ken,

    When I view the various comparator data sheets I find that the upper VICR limitation of VDD - 1 V (25 C) appears to be specific to the TLC prefix comparators. The TLC comparators having that limit are the TLC339, TLC352, TLC372, TLC393 and TLC3702. All of these comparators were developed from about 1983 to 1986, and are legacy devices. 

    The upper VICR limit was likely set as is due to design constraints and the CMOS processes available at the time of the product developments. I checked some of the TLV prefix comparators and their VICR high end is the positive rail, or higher. Those comparators were developed much later in time and use newer CMOS processes.

    It does appear from Kato-san's evaluation that the TLC393 output was attaining the expected state a higher level VDD, but didn't hold as VDD was lowered. Therefore, your experience attaining the correct state when holding at least one input within the VICR range may have been related to the particular comparator you were evaluating, or the VDD level. 

    Thank you for your comments regarding Kato-san's E2E inquiry!

    Regards, Thomas

    PA - Linear Applications Engineering