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Original question:

TLC5540

TLC5540: For (0-5V) ref voltage configuration, center the Analog input signal to 2.5V and swing of max +/- 2.5V

Abhishek Kumar10
Prodigy 110 points
Part Number: TLC5540

Hi,

I read in earlier E2E post that it is recommended to center the signal to 2.5V and swing of max +/- 2.5V when TLC5540IPW  is used in (0-5V) ref voltage configuration. We are planning to use this ADC with 0-5V configuration so that we get a 5V analog input span but we are not clear what is the necessity to have a centered signal at 2.5V? Could you please clarify more details as to why it is required or any signal between 0-5V when fed as input to ADC shall be converted to 8 bit digital in this configuration. 

Please find below the link of earlier post which I am referring to for your reference.

https://e2e.ti.com/support/data-converters/f/73/p/239741/840711#840711

Thanks & Regards

Abhishek

  • 0
    TI__Guru* 91947 points

    Abhishek,

    The full scale output (11111111) will occur when Vin = VrerT. The minimum output (00000000) will occur when Vin = VrefB. The difference between Vreft and VrefB determines how fine or coarse the transition is between codes. For example, if using Vret of 2V and Vrefb = 0V, one LSB = 7.8125mV. For Vreft of 5V and VrefB = 0V, one LSB = 19.53mV.

    If you want to use 0 - 5V analog input, VrefT must be 5V and VrefB must be 0V. Mid-code (10000000) would occur at 2.5V. Thus for this case, if the analog input is a sine wave swing from 0 to 5V, it must be centered at 2.5V. Otherwise, clipping will occur and the input will exceed the data sheet recommended specifications. This does not mean the signal always has to be centered at 2.5V if this is what you are asking. Only when a full scale input is applied.

    Regards,

    Jim   

  • 0 in reply to jim s
    Prodigy 110 points

    Hi Jim,

    Thanks a lot for your response! I am now very clear on the usage and my doubt is answered. I also wanted to ask you that do you have any test data or application information of this IC in which it is used with 5V analog input span.

    I am asking this because when I was trying to find the same in datasheet or any other application notes, I could not find any thing so it will be helpful if TI has done some testing so that I can use that as a reference to get more confidence to use this IC in our design.

    Thanks & Regards

    Abhishek

  • 0 in reply to Abhishek Kumar10
    TI__Guru* 91947 points

    Abhishek,

    We do not have any of this data you have requested. I would suggest maybe ordering an EVM and try this yourself.

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 110 points

    Hi Jim,

    Could you please check once from your side and confirm any other ADC part as well which has 0-5V analog input span with 8 bits or more resolution in Flash or semi-flash type.

    And it will be good if you suggest a part with some application note which also has test data give with this 5V input span range.

    Thanks & Regards

    Abhishek

  • 0 in reply to Abhishek Kumar10
    TI__Guru* 91947 points

    Abhishek,

    Our group does not have any other parts that will support 0-5V analog input range. Please check with the Precision ADC's and Isolated ADC's forums.

    Regards,

    Jim