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ADC08131BIN(EOL) - VREFC

Hirotaka Matsumoto
Guru 27565 points

Hi all,

Would you mind if we ask ADC08131BIN?

Of course, we know that ADC08131BIN is EOL, so this question is relation to only existing system.

<Question1>
Does VrefC of ADC08131BIN receive 5.0V?
Or, the datasheet shows "For the ADC08131, the output of the on-board reference is internally tied to the reference input."
So,Vref is 2.5V, isn't it?

<Question2>
It is relation <Question1>, if VREFC can accept 5.0V, can SDO output 5V(in case of Vin+=5V)? 

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Genius 16890 points

    Hello,

    Answer 1:  Referencing the ADC08138 Function Block Diagram on page 13 of the datasheet, for the ADC08131 VREFOUT and VREFIN are tied together internally.  This point is brought out and named VREFC for the ADC08131.  This means that this pin is 2.5V.  You cannot put 5V on it.  The VREFC pin is used for putting a bypass cap on the reference.

    Answer 2:  You cannot put 5V on the VREFC pin.  The level of DO depends on the VCC and the amount of output current.  See the Digital and DC Characteristics on page 4 of the datasheet.  If VCC = 4.75V and Iout is -10uA, the high level will be 4.5V (min). 

    Mike

  • 0 in reply to Michael Stout
    Guru 27565 points

    Mike san

    Thank you for your so prompt reply and your cooperation always!

    OK, we got it.
    Just in case, please confirm two points.

    VREF is 2.5V, that's why the maximum output(DO's data) is 2.5V, right?
    And  then, is VREFC pin possible to be left floating(open) or should be bypassed with 100uF capacitance?

    Kind regards

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 16890 points

    Hello,


    The VREF sets the maximum input voltage. When VREF is 2.5V that means that the maximum input can be 2.5V because 1LSB = VREF/256.  With an input of 2.5V the output code will be 0xFF.  The VREF value does not affect the DO voltage level.  The DO is a digital output and it's maximum value is dependent on the value of VCC and the output current as described in the datasheet, page 4, VOUT(1).  

    It would be best to have a bypass cap of 100uF on the VREFC pin. 

    Mike

  • 0 in reply to Michael Stout
    Guru 27565 points

    Mike san

    Thank you for your kind reply!

    OK we got it.

    Kind regards,

    Hirotaka Matsumoto