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TLV1805: Part Number Suggestion

Shifali N
Expert 2040 points
Part Number: TLV1805
Other Parts Discussed in Thread: TLV4051, TLV4041, TL331, TLV7011

Hi Team,

The main power input in my design is 12V. I need to monitor this 12V power and generate the PGOOD signal using a comparator with hysteresis.

The comparator should generator power good when supply voltage is more than 10.5V. The comparator output is connected to a FPGA which can accept voltage level of 3.3V. 

Can you please suggest me a comparator (with hysteresis) part number which can be used to monitor input voltage of 12V and generates output voltage that can be connected to a 3.3V IO signal.

  • 0
    Guru 242930 points

    Do you have a reference voltage, 10.5 V or something else?

    If you do not already have a reference voltage, use a comparator with integrated reference like the TLV4041/TLV4051. Run it from the FPGA's 3.3 V supply, and use a voltage divider to scale the input down from 10.5 V to the internal reference voltage.

  • 0
    TI__Mastermind 49836 points

    Hello Shifali,

    Will the comparator be running off the 12V supply? Or the 3.3V supply?

    There are many ways to do this, so there are several options. Clemens mentioned the most common way.

    Are there any "critical" specs (other than accuracy), such as size or power used?

    How much hysteresis? What are your expected trip points?

  • 0 in reply to Clemens Ladisch
    Expert 2040 points

    Hi Clemens,

    I don't have any reference voltage. I just have two voltages in my board. Power Input is 12V and 3.3V IO voltage for FPGA. 

  • 0 in reply to Paul Grohe
    Expert 2040 points

    Hi Paul,

    1. Regarding the supply, just needed the clarification. If I power the comparator with 12V, will the output level also be 12V? 

    2. There is no restriction on the size and power used.

    3.My trip point is 10.5V. The comparator output should go low if supply voltage of 12V drops below 10.5V.

  • 0 in reply to Shifali N
    Guru 242930 points

    1. If the comparator has a push/pull output, then the high output voltage will be 12 V. If the comparator has an open-collector or open-drain output, then the high output voltage is determined by the pull-up resistor, i.e., this can be used for level shifting.
        If the comparator is powered by 3.3 V, then you can use a push/pull output.

    3. You need some reference voltage. You could use the 3.3 V supply (if it is accurate enough), or a comparator with an internal reference.

    What should happen if the input voltage is off? (I.e., is it even possible for the comparator to be powered from the input?) It looks as if the best solution is still the TLV4041. (Use the TLV4041R5DBVR, and a 100 kΩ/4.99 kΩ divider.)

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 23395 points

    All good suggestions from everyone.  thank you

    Paul

    While you have been given some good options so far which include a comparator with integrated reference, I think you could also just divide down the 3.3V you have available to create the reference.  it really comes down to the accuracy of the 10.5V threshold.  here is the concept I am referring to where I used our TLV7011.  Since operating from the 3.3V supply, it is best to use a comparator with rail to rail input.  If you prefer to power the comparator from the 12V supply that is being monitored, we could use a device such as TL331.  Really depends on your system preference.  I  attached the simulation file so you can adjust to your liking,  In this use case, I make the output go low when the 10.5 threshold is reached and I assumed a 0.5V hysteresis level for recovery so the output doesn't chatter if the voltage slowly reaches 10.5V.  Hope this helps.

    Chuck

    TLV7011_UV.TSC