• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 46 subscribers
  • Views 441 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADC12L080: The perform of ADC12L080

随缘
Prodigy 30 points
Part Number: ADC12L080

1. Is the full scale of this ADC is 4*Vref when it works with two differential input? The scale of input defined in the table 1 and the description in the previous paragraph"Each analog input signal should have a peak-to-peak voltage equal to the input reference voltage, VREF , be centered around V REF and be 180° out of phase with each other."  are not accordant.

2. If the input of Vin+ and Vin- are not reach to Vref, the output binary code is centered on 2048?

3.Is the Vcm changeless, and the input on Vin+ and Vin- centered 0V is ok or the circuit should ensure the input on Vin+ and Vin- is centered Vcm?

  • 0
    TI__Mastermind 43830 points

    Hi 随缘

    I'm looking into the answers to your questions.

    I will respond later today.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    TI__Mastermind 43830 points

    Here are my answers to the questions:

    1. The full scale input range is 2*Vref Vpeak to peak. For Vref = 1V this gives Vin_fs = 2Vpp differential. Referring to Figure 3 Transfer Characteristic this shows that for maximum output code the differential input voltage is 1*Vref and for the minimum output code the differential input voltage is -1*Vref. For the Vref=1V case this is +1V differential to -1V differential.
    2. The output code will be 2048 when the input differential level (Vin+ - Vin-) is 0V.
    3. The input common mode voltage (Vcm) is allowed to be in the range of 0.5V to 2.0V. For best ADC performance the common mode voltage should be a DC voltage in the 1.0V to 1.8V range (specification table values are with Vcm = 1.65V). See Figures 18 and 19. For Vcm to be DC means that Vin+ and Vin- are equal and opposite voltage levels above and below the Vcm voltage, so the instantaneous average of Vin+ and Vin- is Vcm.

    The Signal Inputs section of the datasheet along with Figures 38, 39 and 40 describe the input requirements and ways to drive the analog inputs as needed for best performance.

    I hope this is helpful.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 30 points
    Hi Jim B
    Thank you for your answer. But, there are some questions that I can't understand.
    1, The scale of the differential input described in Table 1, Input to Output Relationship—Differential Input indicates the input scale of differential signal is -2Vref ~ +2Vref. While, the previous paragraph says that" Each analog input signal should have a peak-to-peak voltage equal to the input reference voltage, Vref , be centered around Vref and be 180° out of phase with each other."
    2, There is not a common mode voltage input on ADC12L080, Whether the input differential analog signals should be (Vcm+ Vin) or they are Vin and the chip adds a Vcm to the input itself?
  • 0 in reply to 随缘
    TI__Mastermind 43830 points

    Hi

    1. After reviewing the FUNCTIONAL DESCRIPTION section again I see the cause of the confusion. The information in Table 1 conflicts with the input range described elsewhere in the datasheet. The values in Table 1 and Table 2 are 2x larger than they should be.

    2. You are correct, there is no Vcm pin (input or output) on the ADC12L080. For this device Vcm = (Vin+ - Vin-)/2. Vin+ and Vin- should be driven to give a resulting Vcm voltage that is constant and in the range I described previously (1.0V to 1.8V) for best performance.

    The chip does not add any Vcm voltage to the applied inputs. Vin+ and Vin- go directly to the input sampling circuitry of the ADC.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 30 points

    !Hi Jim B:

    Thank you for your patience and response. I am very sorry that I was too busy yesterday to reply to you. With your help I know how to use this device. Thank you once more!

    Best wishes!

    Li Xun