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LM339: LMx39x, LM2901xx Quad Differential Comparators

Chaithra K C
Prodigy 150 points
Part Number: LM339
Other Parts Discussed in Thread: TINA-TI, LMV339, LMH7324, TLV3502, LMV7219, LMV7239, TLV3202, TLV3201, LM2901

Hi,

We have selected LM339 for our application. The frequency of operation for the application is in MHz. (ranging from 1MHz-5MHz). Will the comparator work in these frequency ranges. 

Thank You in advance

Chaithra

  • 0
    Guru 140200 points
    Hi Chaithra,

    a 5MHz signal has a period of 200ns. As the switching times of the LM339 are longer than 200ns, the LM339 is not suited too handle 5MHz signals.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 150 points

    Hi,

    Please give the Switching time range for LM339

    Chaithra

  • 0 in reply to Chaithra K C
    Guru 140200 points
    Hi Chaithra,

    please see section 7.9, 7.10 and 7.11 and figure 4 and 5 of datasheet.

    You can also run a TINA-TI simulation with the LMV339, which is similar to the LM339 refering to switching speed.

    Kai
  • 0
    TI__Guru 54966 points

    Hello Chaithra,

    Please see the attached presentation about toggle frequency

    The fastest the LM39x family can respond is about 500ns (with a large input signal). The slowest is about 1.5us.

    The maximum toggle frequency is at minimum two times the prop delay, or 3us. 1/3us = 333.3kHz. Even at the fastest at 500ns, that is 1/1us = 1MHz, but that does not include the effects of rise/fall time, which is affected by the output pull up resistor and load capacitance. These also depend on the supply voltage.

    At best I would say 250kHz is about as high has you want to go with the 339. So, no, the LMx39 is not suitable for 1MHz.

    Working backwards, if you want 5MHz: 1/5MHz = 200ns, so you want a comparator with a response time less than 100ns.

    Allowing for variation, I would look for a device with a prop delay <75ns. At these frequencies, I recommend a push-pull output for a symmetrical output.

    Unfortunately, there are not many "fast" quad devices (only one, the LMH7324, but it is overkill). There are many duals that would work.

    What is your supply voltage? What is your input signal?

    I would take a look at the following devices first. All should work up to 5MHz just fine.

    TLV3202, TLV3502, LMV7219 and LMV7239

    Comparatorr_Toggle_Freq.pdf

  • 0 in reply to Paul Grohe
    Prodigy 150 points

    Hi Paul Grohe,

    We are ok to use dual comparator.

    Please suggest any comparator/ opamp that can work for below mentioned specifications.

    The input signal specifications are as depicted in the attached pictures.

    We want any device that converts 1.5V to 5.3V input voltage to 5V and 0 to 0.8V ( or below 1.5V ) to 0 for frequency ranging from 1MHz to 5MHz.

    Best Regards,

    Chaithra

  • 0 in reply to Chaithra K C
    TI__Mastermind 24850 points

    Chaithra

    The TLV3201 and tlv3202 should be good options for you. The 3201 is the single channel and 3202 is a dual.

    This comparator family has propagation delay of 40ns.

    Chuck

  • 0 in reply to Chuck Sins
    Prodigy 150 points

    Hi,

    Also there is this signal with characteristics as mentioned in Picture below.

    Please suggest any Opamp / Comparator that can work in this range.

    Thank You 

    Chaithra

  • 0 in reply to Chaithra K C
    Guru 140200 points

    Hi Chaithra,

    I have made a TINA-TI simulation for you:

    Kai

  • 0 in reply to kai klaas69
    Prodigy 150 points

    Hello kai klaas69,

    Thank You for the Simulation.

    What is the input you have given and at what frequency?

    If VM2 and VM1 are Voltage Measurement Meters, How to make it out in the Gragh (which color represents input and output)?

    Also, you are taking Vref( non-inverting termainal) to be 3.26V. I wanted it for 1.5V. what will be the output if both Vref and Vin are at same voltage level.

    Can this Comparator work for 0.3us(Trigger Input) and 3us(Reply Video) pulse duration.

    Please Help!

    Thank You

    Chaithra

  • 0 in reply to Chaithra K C
    Prodigy 150 points
    Please note the Pulse duration may vary from 0.3us to 3us.
    Thank You
  • 0 in reply to Chaithra K C
    Guru 140200 points
    Hi Chaithra,

    I tried to simulate your pulses: High level = 5.3V, low level = 0V, high time = 300ns, low time = 1.75µs, period time = 2.05µs. It's the bright green graph.

    Then there's a voltage divider at the input of TLV3201, made of R1/R2, in order to decrease the 5.3V pulse down to 4.97V. This, to keep the input voltage smaller than the supply voltage. It's the brown curve.

    Next, I generate a reference voltage (threshold voltage) of 1.087V from the 5V supply voltage by the help of another voltage divider R4/R3.

    The dark green curve is the output signal of TLV3201.

    This simulation was only made to check whether the comparator is fast enough for your application. It is!

    You can change the polarity of output signal by just reversing the inputs. And you can vary the threshold voltage by changing the voltage divider.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 150 points

    Hello kai klaas69,

    Can we use LM2901 as replacement to TLV3202 for the same requirements.

    Thank you in Advance,

    Chaithra

  • 0 in reply to Chaithra K C
    Guru 140200 points
    Hi Chaithra,

    I think the LM2901 is not fast enough.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 150 points

    Hello Kai klaas69,

    How about repalcement IC for TLV3202.

    Best regards,

    Chaithra

  • 0 in reply to Chaithra K C
    Guru 140200 points
    Hi Chaithra,

    the TLV3202 should work.

    Kai