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Choosing the right ADC-Driver Amplifier for the ADS5482

Kai Mohrhenn
Prodigy 30 points
Other Parts Discussed in Thread: ADS5482, THS4131, THS4541, THS4551

Hey guys,

i need the right FDA for driving the ADS5482. Its just a one channel system, i don`t need any gain adjustments or other features just a simple single ended to differential amplifier which gives the best possible result referred to system accuracy and driving the ADC. It shall be used for capturing a higher voltage 2MHz Signal which has some less powerfull harmonics up to 50Mhz. The signal can be easily conditioned to the right amplitude to fit the requirements of the ADCs input range, i will use a low order Bessel AAF to be sure that there are no high frequency signals above the nyquist frequency..


Any recommendations?

Greetings from austria!

  • 0
    TI__Genius 13935 points

    Hello Kai,

    I would look at the THS4131 first, it can accomodate up to +-15V supplies.  Other options may be the THS4541 and the THS4551 (both take only 5V supplies maximum though). 

    Higher voltage inputs can be accomodated with resistor divider inputs which may or may not be necessary depending on how large your input voltage is.

    Regards,

    Loren

  • 0 in reply to Loren Siebert 1
    Prodigy 30 points

    Hey Loren, thanks for the answer!

    Yes i will need resistor devider.. ;) The THS4541 looks like a good choice. Do you have any explanation why you have recommended this (and the other ones) ? I`m still trying to improve my knowledge and an explanation would be wonderful!

    Thanks you very much!

  • 0 in reply to Kai Mohrhenn
    Prodigy 30 points
    What i`ve already learned in chosing the right ADC-Driver is that it should have a Gain Bandwidth Safety Margin of 40dB, must be able to provide enough output current for the adcs input and must be able to deliver 3Vpp at the output to fit the fullscale Input Range of the ADS5482. Furthermore the SINAD level should be the same or even better than from the ADCs itself. To give you some more information the Input signal is a transient wave alternating from around -300 to 300V.

    Greetings!
  • 0 in reply to Kai Mohrhenn
    TI__Genius 13935 points
    Hello Kai,


    The ADS5482 requires a 3Vpp signal centered at 3.1V common mode. This pretty much rules out the THS4541. The THS4541 runs on a 5V supply and is best with output signals centered at 2.5V +- 0.5V. With a 3Vpp signal and a 3.1V common mode the outputs will swing to 3.85V at signal peaks. At this amplitude signal lnearity will not be ideal. If you can use a 2Vpp maximum signal into the ADC the THS4541 would be adequate.

    The THS4131 can run on a larger supply voltage and will have more margin on output swing if you select the supply voltages correctly.

    I am not sure about th e 40dB Gain Bandwidth Safety Margin. Normally what you will look for is the ability to drive a signal at -2dBFS with linearity that is adequate for your system. It is not necessary for the amplifier to beat the ADC on specifications, but rather the amplifier and the ADC should both be about 6dB better than your total system specification.

    With a +-300V system your main noise will be from the resistor divider at the amplifier input. You may want to include protection diodes between the resistor divider and the amplifier to protect the amplifier inputs. This is not my specialty so I've included a link to our product page:

    www.ti.com/.../esd-emi-protection-overview.page

    One of the reasons I recommended the THS4131 is that it will be more resistant to voltage transients than the THS4541, which is otherwise a superior amplifier.

    In the past ADC technology was usually the limiting factor in system design. That is no longer the case. ADC technology has developed to the point that it is usually easy to find a good ADC for any design. Because this is the case it is important to select an amplifier based on your system requirements and not on the ADC specifications.


    Regards,
    Loren