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RC4580: Concern of Phase Reversal

hideyuki sakai
Mastermind 6250 points
Part Number: RC4580
Other Parts Discussed in Thread: LM2902

Dear, Sir.

I wonder RC4580 has the concern of phase reversal when input voltage

was invalid such as that happening on LM2902?

Sorry to disturb your job about this kind of matter. Please give your advice.

Best Regards,

H. Sakai

  • 0
    TI__Guru* 84915 points

    Hi, Sakai-san,

    For the RC4580, there shouldn't be issues on the phase reversal when you have an invalid input voltage. However, it is important to mention that you need to verify the output vs input linearity. In the typical application section, the device is configured in differential mode. This configuration results in a unity gain from 2V to 10V. Any value outside this range may result in a saturation voltage. So, it is always important to verify the valid range for your application.

    Please let me know if you have additional questions or comments on this.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Mastermind 6250 points

    Dear, Luis-san. 

    Thank you so much for your valuable information about "Differential mode". 

    I would like to confirm more detail about that. Please give your advice. 

    1)What is the meaning of "Unity gain"? Does it mean 0dB(gain x1) operation? 

    2)Regarding "Differential mode", How to enter into such mode if the customer 

      was using under Noninverting schematic? Negative voltage was applied to IN+

      pin? 

    3)Also regarding "Differential mode", How to escape from "Differential mode"? 

      IN+ voltage was returned to normal voltage? VCC+ off, then on?

    Best Regards, 

    H. Sakai

  • 0 in reply to hideyuki sakai
    TI__Guru* 84915 points

    Sakai-san,

    Please take a look at my responses below:

    1)What is the meaning of "Unity gain"? Does it mean 0dB(gain x1) operation? 

    Yes, it means 0dB or 1x gain.

    2)Regarding "Differential mode", How to enter into such mode if the customer was using under Noninverting schematic? Negative voltage was applied to IN+ pin? 

    The differential mode requires of the two internal operational amplifiers. The RC4580 is a dual operational amplifier. These two amplifiers must be routed accordingly with the figure 13: https://www.ti.com/lit/ds/symlink/rc4580.pdf#page=9

    If customer is using a noninverting schematic, he will be using the circuit configuration that you attached in your previous post. Just remember that the gain will be given by 1 + RF/RIN.

    3)Also regarding "Differential mode", How to escape from "Differential mode"?  IN+ voltage was returned to normal voltage? VCC+ off, then on?

    The differential mode is a particular use case of the RC4580. If customer doesn't require to use differential output, he may use the non inverting circuit like the one you mentioned. In the differential mode circuit from figure 13, the RC4580 may be used to convert a single-ende input into a differential output with unity gain (0dB). A single supply is used in this configuration (Vcc+ = +15V). 

    Best regards,
    Luis Fernando Rodríguez S.