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TLV7031: Input Undershoot and Overshoot & Incorrect Ton

Zeming Kong
Expert 3515 points
Part Number: TLV7031
Other Parts Discussed in Thread: TINA-TI, TLV3491

Hi there,

My customer is evaluating TLV7031 using below circuit, and he found 2 problems.

1. when output becomes L->H or H->L, there will be a undershoot / overshoot at the VIN- pin. 

2. when he powers up VCC gradually without no input, the output immediately becomes high when VCC>1.6V, but as the datasheet explains, there should be a 200us Ton.

What is the reason and how to solve these problems?

Best,

Zeming

  • 0
    Guru 140200 points

    Hi Zeming,

    1. Such spikes are not unusual with nanopower devices. But it can also be the result of an improper measurement or improper mounting of comparator. Breadboard designs are well known for showing these artefacts :-)

    Use such a scope probe

    and stick the end of ground sping directly into the ground pin of TLV7031.

    Another remedy is to mount a small cap directly from the -input of TLV7031 to its ground pin.

    2. What you observe is just manufacturing tolerances. Keep in mind that the datasheet specifies only typicals. So there can be a large amount of manufacturing tolerances without making the comparator to violate the datasheet specifications. Keep also in mind that the specification assumes a capacitive load at the output of TLV7031 which might need some additional time to be charged. So without a capacitive load the device might react faster.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 10485 points

    Thank you for your support Kai! Your input is extremely helpful.

    Zeming, I would recommend trying Kai's suggestion of reassessing your measurement setup. If that doesn't work then please post any additional problems you encounter on this thread.

    Regards,

    Joe

  • 0 in reply to kai klaas69
    TI__Expert 3515 points

    Thank you very much Kai!

    I will try this method.

    Best,

    Zeming

  • 0 in reply to Joe Vanacore
    TI__Expert 3515 points

    Hi Joe, 

    Thanks for your support. I still have some questions.

    The customer used TINA-TI to simulate this circuit, similar undershoot/overshoot happened, but much lower than the detected value (10mV vs. 180mV). If it is due to the probe, Why did this happen again in the simulation? Is this due to the nanopower device internal structure? 

    Actually he is evaluating TLV7031 to replace TLV3491, but TLV3491 shows a smaller overshoot/undershoot, so he is wondering if it is necessary to use the new product. Do you have any material to explain this?

    And TLV7031 started up when VS>1.17V, but datasheet shows it should starts after VS>1.6V and the 200us POR. Is the VS range manufacturing tolerances also?

    Best,

    Zeming

  • 0 in reply to Zeming Kong
    TI__Genius 10485 points

    Hi Zeming,

    I am still working on getting an answer for you. I will try to answer your questions by the end of business tomorrow (11/17).

    Thanks,

    Joe

  • 0 in reply to Joe Vanacore
    TI__Expert 3515 points

    Hi Joe,

    Understood and thank you very much.

    Best,

    Zeming

  • 0 in reply to Zeming Kong
    TI__Mastermind 23415 points

    Zeming

    You are correct that the TLV7031 wakes up earlier than 1.6V.  In characterization, we have actually seen parts that have started to respond at as low a voltage as 1.0V.  However, we did not find the performance to be consistent enough at these operating levels.  To be conservative, we have warranted our performance starting at 1.6V.  So by the time you reach 1.6V and wait the additional power-up time of 200us, the output is warranted to reflect the conditions on the input.  So this is why the device is showing response at much lower supply voltages.  Hopefully that is only a benefit in your system and sorry if that has caused any confusion in your design efforts.

    Chuck

  • 0 in reply to Chuck Sins
    TI__Mastermind 23415 points

    also, please upload your TINA file so I can see how the analysis is setup and work directly from your file

    thanks

    Chuck

  • 0 in reply to Chuck Sins
    TI__Expert 3515 points

    Hi Chuck,

    Thanks a lot for your reply.

    I will try to get the file from the customer and I will send you via email.

    Best,

    Zeming

  • 0 in reply to Chuck Sins
    TI__Expert 3515 points

    Hi Chuck,

    Sorry for opening this thread again.

    I still have a question. TLV7031 has a power-on-reset function, and this holds on the output low for 200us when Vcc goes over min supply voltage range. The customer tested this function in the simulation but he couldn't watch a operation on the output side like a power-on-reset function. 

    Is this also due to the macro SPICE model? This model cannot present a POR function so he couldn't watch it. 

    Best,

    Zeming

  • 0 in reply to Zeming Kong
    Guru 140200 points

    Hi Zeming,

    the model itself explains what is modelled and what is not:

    By the way, usually the simulation only covers standard operation. And POR functionality is not part of the standard operation :-)

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 23415 points

    Kai's comment is quite appropriate.

    We will definitely look into integrating startup conditions in our models but at this time they are not included.

    Chuck

  • 0 in reply to kai klaas69
    TI__Expert 3515 points

    Hi Kai,

    Thank you very much!

    Understood that SPICE models usually cannot show these special functions.

    Best,

    Zeming