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ADC128S102: ADC128S102 query need help

Star Xu
Genius 9645 points

Part Number: ADC128S102

Hi

My customer need help with ADC128S102.

Because of each ADC input  from 16by1 MUX, there are 16 analog input changing for each DIN.

When DIN is changed, the only first digital out is not correctly worked.

Please review an attached file. You can see control signals,analog inpu and digital output after changing from DIN(0, 0, 0) to (0, 0, 1).

- Analog input : IN1 (data changing: 2V, 1V, 2V)

- digital data input : DIN (=> 0,0,1), for A/D of the second analog input channel.

- SCLK : 11.5MHz (not displayed on the file.

I set DIN like below datasheet after chip selector'falling.

The first digital out is for analog 2V but it is not. It is always about digit 10 regardless of input changing.

The second out is refer to analog input 1V.

And third out is refer to analog input 2V.

When I change DIN, I always get meaningless first digital out.

During same DIN, the 2nd, 3rd, 4th, ..., are changed refer to changed analog input.

I think that there is some wrong control when DIN is changed. But I can not find. Could make me clear this problem?

Waiting for your reply.

thanks

Star

  • 0
    TI__Mastermind 21685 points
    Star,
    I will look into this and come back.
    Thanks,
    Vishy
  • 0 in reply to Vishy Viswanathan
    TI__Mastermind 21685 points

    Star,

    You refer to 16 analog inputs and also 16by1 mux. Are we talking about ADC128S102 or some other device? ADC128S102 has only 8 input channels (so 3 address bits AD2, AD1, AD0 as shown in the timing diagram). Please check and advise. See below functional block diagram from DS.

    Also, note the address bits are bit 3, bit 4, and bit 5 of the control register. So please make sure they are correctly addressed as shown in the picture below.

    Thanks,

    Vishy

  • 0 in reply to Vishy Viswanathan
    TI__Genius 9645 points

    Hi Vishy

    Thanks for your reply.

    The output from 16by1 MUX is connected with only an input of ADC.

    For example, AIN1 has below 16 analog input change.

    And DIN setting is below.

    DIN :  000 for AIN1

             001 for AIN2

             010 for AIN3

    In this case, only the first analog input of each ADC input is not converted to digital.

    The first analog input means below red marked signal.

    I checked control timing, but I can not find what's wrong.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Mastermind 21685 points

    In ADC128S102 when a conversion is in progress, the address of the next input for conversion is clocked into the control register through the DIN pin. So when DIN input changed it is applied to the next conversion. See example below (assuming AIN1 address = b000, AIN2 address = b010, etc.)

    Thanks,

    Vishy