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Original question:

LM339A: LM339APWR 5V VCC 4.5VREF Error trigger Low Level Problem

LM339A: LM339APWR 12V VCC 5V VCM Propagation Delay Time

SUN Chao
Prodigy 100 points
Part Number: LM339A
Other Parts Discussed in Thread: TLC374

Hi TI Experts

When I use LM339APWR ,12V VCC, and the positive Input  5V as reference voltage, and how to make sure the propagation delay time? use the max 1.3us as the worst case propagation delay time as the datasheet? how to make the propagation delay time less  or that to say ,how to  make the comparator operate faster? 

(1)The max propagation delay time 1.3us

(2)How about the high temperature such as 65℃ Ambient temperature that influence the propagation delay time?

Thank you very much!

  • 0
    Guru 243980 points

    As shown in figures 4 and 5, the overdrive has the largest effect on the response time. If you have a slow input signal, there is no overdrive, so you get the worst-case response time.

    To change that, use a faster comparator like the TLC374.

    If you go back to a 5 V supply, you have more faster options.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 23425 points

    Sun

    As Clemens mentioned, overdrive is a large contributor to propagation delay and with 1.3us being a typical number you would need to pad that number by an additional amount if you are concerned about worst case prop delay.  A factor of 15 to 20% for process and temperature variation is a fair number to consider.  Faster devices are also available if your system requires prop delay better than the 1.3us range.  In regards to operating at 12V with a reference of 5V, you can expect the performance to be similar to the test conditions provided in the EC table.

    Thanks Clemens for your continued excellent support.

    Chuck

  • 0 in reply to Chuck Sins
    Prodigy 100 points

    Hi Chunk , Clemens

    Thank you all very much!

    Could you explain more about overdrive? I can not understand the overdrive.

  • 0 in reply to SUN Chao
    Guru 243980 points

    Overdrive is the difference between the two inputs, for a quickly-changing input. A slow input signal does not make a step, so the overdrive is zero when the comparator is switching.