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THS4521 application

Thibault
Intellectual 295 points
Other Parts Discussed in Thread: THS4521, OPA683

Hello,

I'm currently designing an analog amplifier chain, for a power-sensitive application using an 16bit ADC with a 2Vpp input span. I would be a fool not to use the THS4521:  Such performances for a such low Iq!

I have 2 concerns :

1) Vocm specs are a little confusing (typical values outside min/max). Spice simulation seems to confirms the min value (please see the attached document for schematic & results).

2) My app need an high impedance input (>200k), so a buffer is required. But I could hardly see an (voltage feedback) amplifier matching the performance of the THS4521. The closest I could find is the OPA683, but it's not RRIO and noise density is greater. Additionally, this part is quite old (about 10 years).  Why lower power parts are not available? No need? Is there some on the drawing table? I'm not a specialist, but is it possible to "extract"  one of the amp in the THS4521 to make simply a single opamp with amazing noise, quiescent current and similar bandwith and slew rate?

Thanks again for this awesome FDA product... all I need now is a matching op amp :)

Thibault

 

Doc1.doc
  • 0
    TI__Mastermind 27715 points

    Hello Thibault,

    Thanks for your inquiry! I have a few follow-up questions before I offer a recommendation:

    1. Which ADC are you driving?
    2. What's your input signal look like? Required bandwidth? Gain?
    3. Is the 200k input impedance differential?

    Best regards,
    Ian Williams

  • 0 in reply to Ian Williams
    Intellectual 295 points

    Hello Ian,

    1.  I'm using an AD9269 (sorry, I haven't found a matching part on TI portfolio: it's a low power app... but I hope the THS4521 is only the begining of a whole very low power family :)  ). 
    2. The input maximal excursion may be a step from 1V to 4.5V with a settling time to 0.01% of 50ns. The FDA is used as an attenuator to match the 2Vpp span of the ADC.
    3. No, the input is a single-ended, clock synchronous signal, which doesn't support loading. Hence, I need to use some buffering, using the FDA with big resistor value is a no-go (I have also a low margin for noise...) .

    Best regards,

    Thibault

  • 0 in reply to Thibault
    TI__Mastermind 27715 points

    Thibault,

    Thank you for the additional information. I have one further question: what kind of development schedule are you working with?

    Also, regarding your comment about the OPA683's age: if you have concerns about us obsoleting the part, please know that as a rule we do not phase out any of our devices as long as customers are buying them.

    Regards,
    Ian

  • 0 in reply to Ian Williams
    TI__Mastermind 27715 points

    Thibault,

    Let's continue this discussion offline. Please e-mail me at ian@ti.com.

    Best regards,
    Ian W.