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TLV172: Using as a comparator

NAOKI AOYAMA
Guru 11215 points
Part Number: TLV172
Other Parts Discussed in Thread: TLV1805-Q1, OPA197, TLV9062, TLV1805

Hello,

Our customer are searching for a single logic buffer.

They need a 18V operation, handling 40kHz square wave, push pull output, mounted in a small package and low cost.

I found the TLV172, have a question.

There is the back to back diodes between IN+ and IN-.

When the customer use the TLV172 as a comparator, a current flow through these diodes.

The customer use the external resistor as 100kohm. So the input current will be less than 10mA.

Is it possible to use the TLV172 as a comparator?

Best Regards,

Naoki Aoyama

  • 0
    TI__Mastermind 49916 points
    Hello Naoki,

    We generally discourage using an op-amp as a comparator, mainly due to the input problems and poor performance compared to a "real" comparator. I'll let the op-amp guys discuss the suitability of the TLV172.

    We have just come out with a new 40V, 250ns, Push-Pull output comparator, the TLV1805-Q1. An 18V, 40kHz square wave should be no problem for it.

    We are coming out with the "Q1" automotive grade first, but will be following with the commercial grade next year. It is sampling now.
  • 0 in reply to Paul Grohe
    Guru 11215 points
    Hello Paul,

    Thank you for your fast reply.
    I will wait for your discussion.

    Regards,

    Naoki Aoyama
  • 0
    TI__Genius 15410 points

    Hello Naoki,

    I do not recommend using the TLV172 in a comparator configuration because of the internal back to back diodes.

    The OPA19x family of devices, like the OPA197, are high voltage devices that do not have internal back to back diodes and can be configured to operate as a comparator.

    If the customer can use a lower supply voltage then I recommend taking a look at the TLV9062.

    As Paul mentioned using a op amp as a comparator will have slower response time compared to a "real" comparator due to the overload recovery time and slew rate of the op amp. 

    In section 10.2.2 in the TLV9062 datasheet there is measured data of the TLV9062 operating as a comparator. I would expect the OPA197 to have a slightly faster response time due to the faster slew rate of the OPA197. If the customer needs a faster response time than what is shown in the TLV9062 datasheet I recommmend using a "real" comparator that Paul recommended.

    Thank you,

    Tim Claycomb

  • 0 in reply to Tim Claycomb
    Guru 11215 points
    Hello Tim,

    Thank you for your reply.
    I see the TLV172 is not recommended to use as a comparator.
    I checked the DS of the TLV1805Q1. It is a good device.
    But it is not in time for the schedule of the customer's project.

    By the way, Why does the TLV172 have the back to back diodes?
    My recognition, it is needed to prevent over voltage break down for bipolar transistor.
    The TLV172 is made by CMOS process, isn't it?

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Genius 15410 points

    Hi Naoki,

    You are correct that the back to back diodes are used to prevent damaging the input transistor in bipolar device. The back to back diodes are also needed for high voltage CMOS devices with the exception of the OPA19x family of devices. Most low voltage (Vs < 5.5V) CMOS devices do not require back to back diodes on the input.

    When does the device need to RTM to meet the schedule of the customer's project? Knowing the timeline will help us recommend a device that may be coming out soon.

    Thank you,

    Tim Claycomb

  • 0 in reply to NAOKI AOYAMA
    TI__Mastermind 49916 points

    Hello Naoki,

    The TLV1805-Q1 is sampling now. You may request free samples from the TLV1805-Q1 web page. The TLV1805-Q1 will fully release to market in December.

    The TLV1805-Q1 and the upcoming commercial TLV1805 will be functionally identical. You may breadboard/qualify with the TLV1805-Q1 version, then switch to the non-Q version once it releases next year.

  • 0 in reply to Tim Claycomb
    Guru 11215 points
    Hello Tim,

    Thank you for your reply.
    I understood the reason why the back to back diodes is needed.

    Sorry, but they need a mass production device now.
    I will introduce and sell it to next project.

    Thanks,
    Naoki Aoyama
  • 0 in reply to Paul Grohe
    Guru 11215 points
    Hello Paul,

    Thank you for your telling me the schedule of the TLV1805.
    Sorry, but they need a mass production device now.
    I will introduce the TLV1805 to next project and another project.

    Thanks,
    Naoki Aoyama