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THS4151: THS2630 is Listed as Drop-in Replacement for THS4151 but the Slew Rate is Much Lower

David Hand
Intellectual 925 points
Part Number: THS4151
Other Parts Discussed in Thread: THS2630, THS4131, THS4130, THS4150, THS7001

Tool/software:

We're planning on using a THS4151 in a new design, but are a bit worried since it is an older part. The THS2630 is listed as a drop-in replacement. It does have the same footprint and pinout, same voltage rails etc. Some of the noise specs are better.

However, the slew rate of the THS4151 is 650 V/us while the THS2630 is only 75 V/us. So it does not appear to be a drop-in replacement if for applications that need the higher slew-rate.

Is it safe to use the THS4151 in a new design? If not, hopefully higher slew rate variations of the THS2630 will become available.

I realize I may not be able to get an answer, but thought I'd ask anyway.

  • 0
    TI__Mastermind 24529 points
    • Hello David,

    Your question is absolutely both a good one and one we can help answer. 

    I will check with my team and we may have some follow up questions for you. 

    Are you able to share any waveforms or signal amplitudes and frequencies with me?  I am curious what your target slew rate would be, or if the THS4151 is at the ideal performance level for your system?

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Intellectual 925 points

    Hello Alec,

    Any help would be greatly appreciated. Our maximum frequency is 2MHz (though typically around 800 KHz) and 20Vpp max amplitude (A = 10V). So we would set VCC to +-15V. So the required slew is 2 * pi * F * A = 125V/us.

    Although the THS4151 states the slew is 650 V/us in the features (which is fine), reading the fine print and looking at the plots it varies with VCC, temperature and output voltage. But it still seems fine.

    The THS2630 on the other hand, just gives the slew 75V/us at VCC = +-5V and provides no more information. It is a pretty new chip. It may well be higher at VCC = +-15V.

    Also, the THS4151 is one of a series of compatible chips, including the good old THS4131 with a slew of 52V/us. The THS2630 is listed as a drop-in replacement for the THS4131 as well (and is better in almost every respect).

    Perhaps the THS2630 is just the first in a series of compatible chips, some of which would be higher slew rate? I'm guessing that is not information open to the public, but it would be nice to know that the THS4151 is not going to go away until such a true drop-in replacement existed.

    Thanks,
    Dave

  • 0 in reply to David Hand
    TI__Mastermind 24529 points

    Hello David,

    You are all-clear to design-in THS4151.  While this is an older device, you are okay to use it for a new design.

    If there is ever a concern on volumes or quantity available, those conversations would occur on a (rare) as-needed basis.  I would rather you design with the preferred part which meets your specs.

    Also, incidentally, the THS2630 is not a dual op-amp but a fully differential amplifier (FDA).  The architecture and function differ and would require different considerations should we discuss a design-in for that device.  If the specs do not work for you, such as slew rate, it would be better to keep THS4151.

    Slew rate is modelled for the THS2630 so you can take a look at our provided SPICE models to see what would be limiting in your system.

    EDIT: strikethrough of earlier inaccurate statement, see later conversation posts.  THS415x, THS413x, and THS2630 are all FDAs which share architecture, pinout, and function.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Intellectual 925 points

    Hello Alec,

    Thanks for the update. Part of your answer is a bit unclear to me:

    Alec Saebeler said:
    Also, incidentally, the THS2630 is not a dual op-amp but a fully differential amplifier (FDA).  The architecture and function differ and would require different considerations should we discuss a design-in for that device.

    The THS4151 is also an FDA. It sounds like you're saying the THS2630 is really not a drop-in replacement (even ignoring slew-rate of course).

    Based on these links and comparing pins etc, I assumed it was ok:

    alternate products with THS4131IDGKR

    alternate products with THS4151CD

    In the case of the THS4131 (which we use in a couple of places), it even has a higher slew rate.

    Are you saying there are issues other than slew rate that would preclude using a THS2630 as a drop-in replacement for parts such as THS4151?

    Thanks,

    Dave

  • +1 in reply to David Hand
    TI__Mastermind 24529 points

    Hello Dave,

    I have committed a classic blunder: multi-tasking and not double-checking what I wrote!  You are absolutely correct here, thank you for catching my contradiction.

    The THS4151 is an FDA also, just as the THS4131 and THS2630 are FDAs.  The THS4150 and THS4130 are the versions with the power down feature.

    The devices are pin for pin & drop-in for all three packages: D, DGN, and DGK.

    You may use these devices interchangeably as long as you pay attention to the specs, including slew rate, noise, offset voltage, and quiescent current.

    I hope this helps resolve my earlier statement and complement my recommendation to use THS4151 if you require the higher slew rate.  If you need help modelling or examining what slew rate your require for your application, I can continue to assist you with those actions.

    Thank you again Dave!  I appreciate you coming back for clarity and challenging my logic so we could find a clear resolution.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Intellectual 925 points

    Alec,

    Thanks for the help. We'll go ahead and use the THS4151.

    TI does seem really good at not just stopping production of a part unless there is a replacement. The board this new one is replacing uses some even older parts (eg THS7001), which, though they do not show up in your product tables, are still available. 

    Regards,

    Dave

  • 0 in reply to David Hand
    TI__Mastermind 24529 points

    Hello Dave,

    Great to hear you were able to make a decision and feel supported in that decision. 

    TI does not end production of devices at a certain year-mark or level, we work to help our customers (such as yourself!) meet their needs across our portfolio.  As you mentioned, some devices are still available but may not be promoted for new designs, etc.

    In the case of THS415x, we present the THS2630 as an updated device to use if your circuit design is improved or kept to similar performance.  For your design, the slew rate is a key spec and the THS4151 is the better recommendation. 

    Please do not hesitate to reconnect on future questions.  Thank you Dave. 

    Best,

    Alec