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OPA1632

EE_MT
Intellectual 390 points

Other Parts Discussed in Thread: OPA1632, TINA-TI

On page 6 (Figure 1) in the datasheet of the OPA1632:

1. What is the purpose of R5 and R6 (40 ohm resistors)? 

2. If there was no C3 (2.7nF, differential Cap), would you still include R5 and R6? 

Thanks

  • 0
    TI__Genius 13935 points
    Hi Matt,

    Can you confirm the figure number and page? The online datasheet does not seem to match your description of Figure1.

    I found a figure 14 on page 13 that may be the figure you are referring to.

    In Figure 14 the 40 Ohm resistors are part of a low pass filter and also ensure stability of the amplifier with the 2.7nF filter capacitor.

    If the capacitor C3 were not present R5 and R6 may still be needed depending on the ADC input capacitance.

    If you eliminate C3 there will be more broadband noise at the ADC input. The OPA1632 has a lot of bandwidth compared to the audio channel.

    Regards,
    Loren
  • 0 in reply to Loren Siebert 1
    Intellectual 390 points

    Thank you for the reply Loren.

    You are correct, in the TI Datasheet, the figure that I am referring to is on Page 13, Figure 14. I somehow opened the old  Burr-Brown Datasheet. 

    The output of the OPA1632 will be connected to an Instrumentation Amplifier - sending a small AC signal to another board. The input of the Instrumentation Amplifier has a differential 1kHz LPF so I do not need any additional filtering. However, I do not know whether R5 and R6 are necessary for the OPA1632's stability if the OPA1632 contains a LPF (C1 and C2 are present, no C3). 

  • 0 in reply to EE_MT
    TI__Genius 13935 points
    Hi Matt,

    If C1 and C2 are present it is best to at least leave place holders for R5 and R6.

    If you want to simulate the circuit in TINA-TI you can test the stability under different conditions. The OPA1632 is contained in the built in library in TINA-TI.

    Regards,
    Loren