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TLV9002: A discrete FDA design

Yue TANG
Expert 8485 points
Part Number: TLV9002
Other Parts Discussed in Thread: THS4521, THS4520, THS4551

Hi,

My customer want to use TLV9002 to design a FDA to replace below THS4521 design.  can you please help on this thought?  thanks. 

3414.1.TSC

 

  • 0
    TI__Guru*** 140136 points

    Yue,

    THS4521 is Bandwidth: 145 MHz (AV = 1 V/V) Slew Rate: 490 V/µs and TLV9002 is Unity-gain bandwidth: 1 MHz.  I see the simulation is 50Hz.

    What is the purpose of the 760mV supply?

    Here is a start. It still needs some tweaking.

    9002.TSC

  • 0 in reply to Ron Michallick
    TI__Expert 8485 points

    Ron. 

    Thanks for the design , it's helpful.  About the 760mv, I will check with them. basically, it is a bias.

  • 0 in reply to Yue TANG
    Guru 47535 points

    So Yue,

    I looked at that original THS4521 ckt - those are very high R values for a bipolar input FDA. If you need to use those, you might consider a CMOS FDA - kind of rare, but look at the 

    THS4520 or THS4521, 3.3V CMOS FDA's. The FDA provides a lot of advantages in how simple it is to set output CM voltage - I also notice a seperate op amp to drive the CM with Vcc/2. Most FDA's will default internally to Vcc/2 without an external driver - just needs a decoupling cap, not sure that is the case on the THS4520. 

    If you don't need to use those very high R's, move those down and look at the much improved (over the THS4521) THS4551 FDA. 

  • 0 in reply to Yue TANG
    TI__Guru*** 140136 points

    Yue,

    Here is circuit that needs only one TLV9002 and it shifts the output to center the -90mV input offset. If the 90 mV offset is useless information then I would suggest making the input AC coupled and making R1 and R6 200k ohms. Note V2 is not needed.

    9002(#2).TSC