AD7819 missing datasheet information.

I have to run the AD7819 with VDD 5 V and interface to 3.3 V tolerant inputs at the digital side. Max logic output voltage is not specified in the data sheet. The DB7..0 is specified to be TTL

compatible and the BUSY signal is not specified at all. What is the Max output voltage these outputs can have with 5 V VDD?

  • 0
    •  Analog Employees 
    on Oct 1, 2018 8:11 AM

    Hi,

    AS7810 datasheet says that it is TTL compatible. It is characteristic of a TTL logic to have voltage levels range from 0 to Vcc/Vdd. Typically, logic "0" is created at voltage range of 0V to 0.8V while Logic "1" at 2V to Vcc/Vdd.

    AD7819 is specified to operate from 2.7V to 5.5V Vdd. For logic input, 0V to 0.4V is consider as LOW but the range increases to 0.8V if the Vdd is 5V. While 2.0V to Vdd input voltage will be consider as HIGH.

    For Logic Output, AD7819 will give 0V to 0.4V for logic "0" with maximum of 200 µA sinking current while for Logic "1", it will give Vdd down to 2.4V if the current sourcing reach up to 200 µA.

    If you supply the AD7819 with 5Vdd and the controlling device or MCU has high input impedance, the output logic voltage of AD7819 will go as high as 5V. You have three option to choose to address the problem. One is to use a level translator. Second is to change Vdd to 3.3V but retain the 5V supply on the Vref. Last option is to use voltage divider on the output of the AD7819 using resistor to reduce the voltage.

    Regards,

    Daryl