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TLV3501: schematic review of TLV3501

Jimmy Lai
Expert 6845 points
Part Number: TLV3501

Dear Team,

  1. Comparator

Input voltage swing is from 3.6V to 0.5V, and it could not be recognized by TLV3501A. Please help review and comment hot to improve to make sure UB2 can recognize and output voltage correctly. Thanks.

 

UB2:

  • Supply voltage: 3.3V
  • Original input voltage is 5V to 0.5V and will clamped into 3.6V to 0.5V by Q5

Thanks a lot,

Jimmy

  • 0
    Guru 298820 points

    What exactly do you mean with "could not be recognized"? What are the input and output voltages? Can you show an oscilloscope trace?

  • 0
    TI__Genius 11701 points

    Hi Jimmy,

    In addition to Clemens questions, I would also like to add that 3.6V is right on the abs max rating of the input voltage range. we do not recommend operating right on the abs max. What happens if the max input is divided further to something like 3.3V?

  • 0 in reply to Chi Nguyen1
    TI__Expert 6845 points

    Hi Chi,

    Thanks for your great support.

    For comparator, it includes two types of input voltage below. I have a couple of questions below

    1. My initial question is how to design a circuitry to support these two input voltage.
    2. For following circuitry, IN1- is set as 1.73V, and the common voltage is set as 1.65V at IN1+. At out pin, it should output 3.3V swing to next device. But resistor is with 5% tolerance, Therefore, how to improve the circuitry?
    3. Can you help explain what the use of the hysteresis feature? Is it useful for our application?

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Genius 11701 points

    Hi Jimmy, we are on holiday break today and will review your post when we are back tomorrow

  • 0 in reply to Chi Nguyen1
    TI__Expert 6845 points

    Hi Chi,

    We appreciated your great support.

    I’ve understood what the use of hysteresis. Let me update these questions as follow.

    1. How to design a circuitry to support these two types of input voltage below?
    2. For following circuitry, IN1- is set as 1.73V, and the common voltage is set as 1.65V at IN1+. At out pin, it should output 3.3V swing to next device. But resistor is with 5% tolerance, Therefore, how to improve the circuitry?
    3. We are going to connect pin#3 and pin#6 via a resistor to add hysteresis feature. Please also advise what the hysteresis window should be.

    Thanks.

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Guru 55306 points

    Hi Jimmy,

    Chi is out until Thursday.

    Is the input signal AC coupled?

    If you do add hysteresis, there should also be a resistor in series with the input (between input and divider) to create the hysteresis.

    Please see the following appnote on hysteresis:

     Non-inverting comparator with hysteresis circuit (Rev. A)

  • 0 in reply to Paul Grohe
    TI__Expert 6845 points

    Hi Chi and Paul,

    Thanks for your great support!

    Typical hysteresis is 6mV and our expected the minimum input swing is 0.225V(0.25V +/-10%). I have no idea if hysteresis is required. Please help advise. Thanks.

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Genius 11701 points

    Jimmy,

    I am not really sure what you are asking for. The typical hysteresis is 6mV which is the internal hysteresis of the device but if you need more, then you need to design for external hysteresis. The process to design for hysteresis is described in the app note Paul referred to. How much of a hysteresis window is dependent on what you or the customer needs. We also have a calculator tool if that helps as well. I also just made an example of a ~350mV hysteresis circuit below. 

    7752.Comparator Hysteresis Tool.xlsx

  • 0 in reply to Chi Nguyen1
    TI__Expert 6845 points

    Hi Chi and Paul,

    Thanks for your great support!

    Regarding the attached file, it looks for 7752 comparator, is it also available for TLV3501? Thanks.

    Please find the attachment.

    7752.Comparator Hysteresis Tool 1.xlsx

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Genius 11701 points

    Jimmy,

    Sorry must have been a typo, yes this tool works for any push pull/open drain devices.

    I noticed you had 50 mV for the internal hysteresis line. That is the internal hysteresis of the device itself (which is 6 mV for TLV3501).  The total amount of hysteresis you desire is inputted via the VH and VL line so I would change 50 mV to 6mV. Other than that it looks fine. 

  • 0 in reply to Chi Nguyen1
    TI__Expert 6845 points

    Hi Chi,

    Thanks for your great support.

    Our required hysteresis voltage is 50mV and related resistance can be derived from the TLV3501A datasheet below. It is different from TI’s tool. Even I use the parameters(derived by TI’s tool) into the formula of the TLV3501 datasheet. Hysteresis voltage is still not similar. Please help confirm. Thanks.

     

    • Resistor(derived from TLV3501 datasheet)

    R1 = 50-ohm

    R2 = 3.42K-ohm

    V+ = 3.3V

     

    • Resistor(derived from TI’s tool)

    R1 = 22E-12 ohm

    R2 = 10K-ohm

    V+ = 3.3V

     

    TLV3501A datasheet

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Genius 11701 points

    Jimmy,

    As I have mentioned before, the VHYST_INT line in the calculator is for the internal hysteresis of the device itself (6 mV). You are already accounting for the TOTAL hysteresis by setting the VH and VL lines. 1.675 - 1.625 is 50 mV. The tool will just create an extra 44 mV on top of the 6 mV internal to create the 50mV. 

    This is what I get from the tools values. Its not super precise but it gets close to the targeted thresholds. You may need to tune it a little if you need it to be more precise. 

    You could also just use the app note Paul referenced earlier to do the hand calculation your self. You would just design for 44 mV of hysteresis since the 6mV is already inside the chip. Non-inverting comparator with hysteresis circuit (Rev. A)