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.

ADS8405

Hi, We use an ADS8405i in the design and for some boards we can't get fullscale input for the ADC. It saturates near 1V instead of 4V. I have verified the Vref that is exactly 4.096V and the 5V is OK. I just see a small ripple of 150 mV on the 3.3V for digital power supply. I believed it was the ADC that was faulty but we have changed it and it's the same problem.Could you tell me what could reduce the scale of saturation of ADC with a clean AC+dc signal below 3.5V ? This ADC is replacing the ADS8401. The signal is fed by a buffer 0-5V  AD8031 with 1KOhms  at the input of the buffer (non inverter) and 15 Ohms to feed the ADC.

  • Hello Mathieu,

    If possible please post the schematic and board layout of the design showing the supply circuitry and the input buffer AD8031.  The 150mV ripple of the digital supply could cause issues where the signal may be coupling into the ground, input or reference connections.  The datasheet elaborates on page 21 on the sensitivity of the device to the glitches on the power supply.  Table 2 has a few recommendations on the decoupling capacitor placement.  Is it possible to experiment with a quiet/low ripple AVDD and BVDD supply to see if the problem is resolved?  Please let me know if the required bypass capacitors are installed in the board.  

    Thank you and Best Regards,

    Luis