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ADS7953: application diagram for an OPA192

Chi Zhang2
Intellectual 1950 points
Part Number: ADS7953
Other Parts Discussed in Thread: OPA365, OPA325

Hi, Expert

my customer want to use ADS7953, and use example application.

some question need to confirm with you:

  1. figure66 in ADS7953 datasheet , customer want to use 3.3V for OP192 power, for 1XVref(only 2,5V), any risk?
  2. customer want use AD8605 to replace OP192, also using 3.3V for 1XVref, is it acceptable?
  3. what is the current through the register connecting OP192? which package is more suitable？

Thanks

BR

Chi

  • +1
    TI__Mastermind 22950 points

    Hi Chi,

    1. Yes this is OK. 

    2. I am not familiar with the AD8605 so I cannot say for certain. We have other cheaper options such as the OPA325 and OPA365 that can also work in this case. 

    3. The current depends on a number of factors such as the sample rate, input voltage and source impedance. 

    Regards,

    Aaron

  • 0 in reply to Aaron Estrada
    TI__Intellectual 1950 points

    Hi，Aaron

    could you help to double check if this schematic is okay or not.

    ADS7953_scheme_0309.pdf

    Thanks a lot

    BR

    Chi

  • 0 in reply to Chi Zhang2
    TI__Mastermind 22950 points

    Hi Chi,

    My comments on the schematic are below:

    • The filter after the buffer doesn't look populated. I recommend populating these components. The resistor is there to mainly help make sure the opamp can drive the capacitive load and prevent oscillation. The capacitor is there to help facilitate settling on the input of the ADC.
    • There looks to be a configurable option to bypass the opamp. I recommend adding the bypass path to the opamp output before the filter. At minimum, there should be an RC filter between muxout and adcin. 
    • During layout, ensure that the bypass capacitors on the supplies are placed as close to the ADC pins as possible. 

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    TI__Intellectual 1950 points

    Hi, Aaron

    Thanks a lot for your advice. there is one more question for application.

    if we take figure66 as an example, we don't need to add a opa in front of ADC_CH as a buffer?

    BR

    Chi

  • 0 in reply to Chi Zhang2
    TI__Mastermind 22950 points

    Hi Chi,

    That really depends on the source impedance. If the source impedance is very high, then the customer will likely need an OPA at the input of each channel. However, if their source impedance is relatively low, <= 500ohms, then the OPA can sit between MUXO and AINP. 

    Regards,

    Aaron