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TLV333: Drive Capacitive Load

user4090349
Intellectual 791 points
Part Number: TLV333
Other Parts Discussed in Thread: TLV9004, TLV376

Tool/software:

Hello

I would like to use TLV333 to make a bias voltage and I would like to check the stability. However, when I try to run AC analysis. The simulation almost run out of work.

Could you help me run TINA of the simulation? if it is not stable, could you help adjust the circuit to make it stable?

  • +1
    TI__Mastermind 19077 points

    User,

    Here is some background and solutions for your problem.

    1. The TLV333 and other chopper amplifiers are generally challenging when it comes compensating for driving capacitive loads.  The main reason is that the output impedance is not flat.  In the case of the TLV333 this issue is exaggerated by the high output impedance.
    2. The attachment below shows a set of compensation components that allow the TLV333 to drive the 1.1nF load using the Riso-dual-feedback topology you show.  While this circuit is stable the large 500 ohm isolation resistance will limit what you can drive.  This may not be a huge issue though as the TLV333 is a low output current devices anyhow.
    3. The plots below illustrate a good phase margin (77deg), good step response (minimal overshoot), and good AC response (minimal gain peaking).

    Riso-Dual-Feedback TLV333.pdf

    Let me know if this helps.  Depending on your goal, I could help find an alternative devices with a flatter and lower output impedance which is more optimized for stability.

    Best regards,

    Art 

  • 0 in reply to Art Kay
    Intellectual 791 points

    Hello Art Kay

    Thanks a lot for the result. Now I understand TLV333 is not suitable for drive capacitive load. In previous design, I use TLV9004. But I like the offset voltage of TLV333.

  • 0 in reply to user4090349
    TI__Mastermind 19077 points

    You may consider any non-chopper that has low offset as an alternative.  I can help you choose an option if you specify:   

    • Cost range - I add this as the choices you selected are low cost, so I think that is a key concern.
    • Max offset
    • Supply voltage
    • Bandwidth, slew rate, power or other requirements that you think are important.
    • The fewer the constraints the more options you will have 

    Once we select an amplifier I can stabilize it.  

    Best regards, Art 

  • 0 in reply to Art Kay
    Intellectual 791 points

    Hello

    Yes, cost is a very important concern. TLV333 & TLV9004 are all very cost-effective part.

    max offset voltage, 20uV

    supply voltage, 3.3V

    bandwidth, slew rate are not important due to the signal is DC

    Thanks!

  • +1 in reply to user4090349
    TI__Mastermind 19077 points

    Finding a low-cost 20uV max offset non-chopper amplifier is challenging.  Cost is 0.365/1k for single channel. The TLV376 has very good offset 100uV max, 40uA typical, 1uV/C drift.  It has a low relatively flat output impedance. It is rail-to-rail input-output.  Below is the stability analysis report.  As expected, this device is much better from a stability perspective.  Alternatively, you can use the TLV333 above, but it is really limited in output  drive due to the very large required isolation resistor.  I hope that works for you.

    TLV376 Riso-Dual-Feedback Stability.pdf

    Best regards, Art