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ADS6445: DC input for ADS6445 and ADS5482

Hirotaka Matsumoto
Guru 27585 points
Part Number: ADS6445
Other Parts Discussed in Thread: ADS5482, , THS4509, ADS5482EVM

Hi all

Would you mind if we ask ADS6445 and ADS5482?

On these EVMs, AC coupling is used for these EVM's input.
Just in case,  ADS6445 and ADS5482 are possible to use with DC-input, right?
We assume that these EVMs only correspond for AC-input.

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Expert 4025 points
    Hello Hirotaka,

    We are taking a look into your question and will be back with you soon.

    -Chloe
  • 0 in reply to Chloe Shay71
    TI__Expert 4880 points
    Hirotaka,

    Regarding the ADS6445 EVM, Though DC coupled analog inputs are not the default. It is possible. For DC- coupling, replace C46 and C47 with 0 ohm resistors and remove R9 and R18. The ADC VCM should be used to set the CM input of the amplifier by making sure R84 is populated with a 0 ohm resistor. Because the ADC has a common-mode voltage of 1.5 V, and because the THS4509 is not a rail-to-rail amplifier, users should adjust VCC to 4 V and –VCC to –1 V, which can be done by applying the respective voltages to J21 and J22.

    Please reference the following user guide for more information.

    www.ti.com/.../slau196.pdf

    Yusuf
  • 0 in reply to Yusuf%20Agoro
    Guru 27585 points

    Yusuf san

    Thank you so much for your advice!
    As the conclusion of customer's confirmation, the customer could realize DC-coupling.

    On the other hand, is it possible to use DC-coupling with ADS5482?
    The device ADS5482 corresponds for DC-coupling, however in case of ADS5482EVM, does it require to modify the EVM board? 


    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Yusuf%20Agoro
    Guru 27585 points

    Yusuf san

    We guess that your days are so busy, however could you give us the reply for our last update?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Expert 4880 points

    Hey Hirotaka, 

    What is driving your need to DC-couple the input signal to this device? What is your input signal frequency/bandwidth?

    Thanks

    Yusuf 

  • 0 in reply to Yusuf%20Agoro
    Guru 27585 points

    Yusuf san

    Thank you for your reply.

    We confirmed your questions from our customer.
    Please refer to follows;

    What is driving your need to DC-couple the input signal to this device?
    ->Our customer would like to use for multiple sensors.
       A few sensors may detect DC signal.
       Therefore our customer would like to use for DC signal detection.

    What is your input signal frequency/bandwidth?
    ->DC to 100kHz

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Yusuf%20Agoro
    Guru 27585 points

    Yusuf san

    Thank you for your help always.

    We assume that your days are so busy.
    We would like to know whether ADS5482 is possible to use for DC-coupling or not.
    So, could you let us know it?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Expert 4880 points

    Hirotaka-san,

    Sorry for the delay. As far as your questions goes. In order to modifiy the EVm to allow DC coupling you will have to remove all of the transformers (T1) and install 0 ohm resistors in their place. (use 0-ohm to bridge 1-6 & 3-4). If your signal is single-ended you will need to use the on boar THS4509 to convert it to differential. If using the THS4509 you will need to change the jumper SJP4 from 1-2 to 2-3 and also remove T2 by using 0-ohm resistors just like T1. You will need to remove C1, C4, C11, & C15 install 0-ohm resistors in their place. You may also need to adjust the filter on the output of the THS4509 to make sure it passes your input signal. More on this in section 2.3.2 in the user guide. You may have to use tina spice to experiment with componenets to find the right response for your application. Also, if you are using single ended you will need to terminate the un-used differential input to the amplifier. I am not completely sure how this is done for the THS4509, but that is a question for the high speed op amp team you can post on their page. Lastly you will need to verify that the common mode voltage at the output of the op amp matches the recommended common mode voltage of the ADC.

    Please let me know if you have any more questions

    Userguide : http://www.ti.com/lit/ug/slau207/slau207.pdf

    Thanks

    Yusuf

  • 0 in reply to Yusuf%20Agoro
    Guru 27585 points

    Yusuf san

    Thank you for your cooperation always!
    OK, we got that ADS5482 is fitable for DC-coupling and EVM requires to modify a lot.


    Kind regards,

    Hirotaka Matsumoto