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TLV1822: Pulse OFF width issue

Ganesh V
Prodigy 90 points
Part Number: TLV1822
Other Parts Discussed in Thread: TLV3502, TLV3602, TLV3202

I am using TLV1822 device as an comparator circuit diagram is attached.

I have faced the issue that, comparator output Pulse OFF time is higher than pulse ON time.

I have checked comparator device alone like input is given to IN+ and Reference voltage ~1.6V given to IN-,

Input frequency is 64Khz 50% duty, still am facing same issue.

 

  • 0
    Prodigy 90 points

    If this device will not support for our requirement kindly suggest us suitable comparator part no.

    Requirement: 64KHz to 2.5MHz frequency. (Vth= ~1.55 and Vtl= ~1.4V) 

  • 0
    TI__Guru 53996 points

    Hello Ganesh,

    Is the incoming waveform a square wave or sinusoidal? What is the typical amplitude across the secondary.

    It is not uncommon for the TPHL and TPLH to be slightly different. As you push the speed limits, this difference becomes more noticeable.

    What is the VCC supply voltage?

    You may need a faster comparator. The max toggle frequency is listed as 500kHz. The TLV1822 family "claim to fame" is the 40V max supply and not really speed.

    For 2.5MHz, you would need a comparator with a prop delay in the <50ns range to ensure symmetrical outputs. Also you may want to use a push-pull output instead of a open-collector as the risetime of a open-collector is determined by the pull-up and load capacitance. Most high speed comparators are push-pull output.

    Have a look at the TLV3202 (40ns), TLV3502 (4.5ns) or TLV3602 (2.5ns).

    Also make sure that the reference voltage is splitting the input waveform exactly through the center. Any distortions or shift in the center-line will change the duty cycle.

  • 0 in reply to Paul Grohe
    Prodigy 90 points

    Thanks for response.

    The incoming signal is square wave.

    supply voltage is 3.3V.

    Are you suspecting this because of speed limit in TLV3202  device.

    Reference voltage is fixed one verified no distortion. 

  • 0 in reply to Ganesh V
    TI__Mastermind 24560 points

    Ganesh

    Thanks for following up.  We will review Monday and get back to you.

    Chuck

  • 0 in reply to Chuck Sins
    TI__Mastermind 24560 points

    Ganesh

    After further review, I concur with Paul's suggestion.  The TLV1822 isn't a good fit for this application especially since speeds can reach 2.5MHz (200ns high and 200ns low).  The prop delay of the TLV1822 is in the 400ns range, so it cannot keep up with such an input.  Please consider other devices such as TLV3202 since your operating supply voltage is less than 5V.  

    Thanks for your support of the forum,

    Chuck