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TLV1704-SEP: OUTPUT during Power-up

Martin Beakes
Prodigy 50 points
Part Number: TLV1704-SEP
Other Parts Discussed in Thread: TLV1701, , TINA-TI

Hi, 

When using the default TINA-TI model provided for the TLV1704-SEP (which is the TLV1701 spice model) I noticed the following behavior. 

As shown below, when using the default model TLV1701 (spice model date : 12/16/2013) , we can see that the output (COMP_OUT) remains LOW during Supply ramp up. 

However, when using the newest spice model from 08/30/2023, we can see that the output goes High and then LOW during supply ramp-up. 

Looking at the image below (COMP_OUT in red) we can see that the comparator drives the output LOW when VCC is about 2.17V.

I also run this simulation using another Spice Simulator and got the same results. 

My assumption is that the newer Spice model reflect the expected behavior of the comparator meaning that the comparator is not able to drive the output until VCC reaches 2V. 

1. During power ramp up, what is the expected state of the output when VCC < VCC MIN (2.2V). 

2. Should we expect the OUTPUT to follow VCC due to the external Pull-up at the output or is the output should be LOW ?

The circuit that I'm using is the same as the one below except  that VCC = 3.3V and I used different resistor values to obtain a different Threshold.

  • 0
    TI__Genius 11701 points

    Hi Martin,

    Thanks for your question. Unfortunately, this device does NOT have power on reset (POR) so its output behavior is considered indeterminate below the minimum operating voltage of 2.2V. In other words, there is no known start up condition so I would not rely on either models to simulate the actual device behavior. Let me see if we have ever collected bench data on the start up behavior of this device so that you could see in general what it looks like. I suspect that it would look something like the new model behavior. 

  • 0 in reply to Chi Nguyen1
    Prodigy 50 points

    Ok thanks. Bench data can definitely help.  

    Looking at the datasheet, Vo is specified to be 0.7V to 1.1V max from power rails. The datasheet mentioned Vs = 36V. 

    In my case, I'm using 3.3V to GND. What will be the maximum output VOL when the comparator drive the output LOW ?  Should I plan for 0.7V to 1.1V ? 

     

  • 0 in reply to Martin Beakes
    Prodigy 50 points

    Question 3:  

    In the datasheet, there is no information about the Pull-up voltage on VOUT of the comparator. 

    Since it's open collector output, is it correct to assume that the output can be pulled-up higher than VCC ?  Can we pull-up to 5V when using 3.3V supply or is there a limitation like VCC+x ?

  • +1 in reply to Martin Beakes
    TI__Genius 11701 points

    Martin,

    Question 1: I was able to see that for a few units, the output was HIGH Z during start up. However, I cannot warranty this start up condition. With that said, i dont expect to see any glitches on the start up.

    Question 2: This is actually a VOL spec (output voltage swing from V-). which is dependent on the pull up resistor and how much current you expect to sink. Therefore, the maximum VOL is 900 mV above V- when the sinking current is 4mA. With that said, I believe this value is a bit conservative and the actual typical value is much lower. I’d use the graph below to estimate the VOL with expected sinking current for typical value and then add 30% for process variation to get the maximum value. So 5V pull up voltage with 1k resistor is estimate to sink 5 mA for a VOL ~300mV.

     

    Question 3: Yes, the output can be pulled up to 36V regardless of supply voltage. 

  • 0 in reply to Chi Nguyen1
    Prodigy 50 points

    Hi, 

    thanks for the quick response. 

    Questions 1:  Ok Thanks this really helps. 

    Question 2 :  Thanks for the answer and the graph this help. 

    Question 3 : Thanks for the answer.