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ADC0803LCN - Full Range Scaling - Help Needed

Evan Walsh
Prodigy 30 points

Hi,

I am using an ADC0803LCN, hoping to convert a 0.5 - 4.5 V range analog signal. I am having difficulty understanding how to adjust the ADC0803LCN for this input range. Could someone help dumb it down a little for me, in particular how to scale for 0.5 - 4.5V range, thank you.

  • 0
    TI__Expert 3355 points

    Hi Evan,

    This is just to tell you that I have received your message, and I am looking into details of this device's operation.

    BTW This is a very old design, and somehow the datasheet on the web has been truncated... sorry about that.

    I will get back to you in a day.

    Sincerely,

    tom

  • 0
    TI__Expert 3355 points

    Hi Evan,

    For this family of devices, for maximum dynamic range, you need to apply the refrenece voltage to the REF/2 pin that is equal to your signal span.

    In you case you signal span is 4.5-0.5 = 4V. Therefore force 4V onto the REF/2 pin. Also bias the IN- pin at 0.5V. Apply your single ended signal to IN+.

    Now when V(IN+) = 0.5V, the output code produced by the ADC will be 0x00.

    When V(IN+) = 4.5V, the output code will be 0xFF.

    You can also keep it simple and apply 5V to REF/2, and ground the IN- input. The ADC will not use some of its range; the codes below 0.5V and above 4.5V will neve occur in ADC output.

    Hope this helps.

    Sincerely

    tom