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ADC121C021: Wrong I2C address selection inputs

Nuno Dias
Prodigy 190 points
Part Number: ADC121C021

Hello,

I need to use up to 5 ADC on a I2C bus. I am using ADC121C021.

According to the datasheet, VSSOP version supports 7 addresses that can be defined by the ADR0 and ADR1 pins. Table 1 (Slave Addresses) refers device is configured with 0x53 I2C address when ADDR1 = GND and ADDR0 = Floating. On the other hand, 0x54 is configured when ADDR1 = GND and ADDR0 = GND.

I'm having different results compared to this table. My devices are responding to 0x54 address when ADDR1 = GND and ADDR0 = Floating or responding to 0x55 when ADDR1 = GND and ADDR0 = GND.

This issue is not a problem for me because I can simply use other addresses. But could you confirm me if there is not  an error in the datasheet?

Best Regards
Nuno Dias

  • 0
    TI__Mastermind 24940 points

    Hello

    This device has been out for over a decade, and we had not had any questions of feedback on the address pins.

    I would initially think that the floating pins would the issue, in case the voltage on the pin is being pulled high or low.

    But from taking a further look into it, it is interesting that the address you are seeing are shifted one down on the table.

    I will take a second look to see if there is any info on the addresses being incorrect.

    I would suggest on your side to double check, just to be sure there is nothing odd going on. such as an unexpected voltage on a pin. and testing the ADC on an empty bus, that way it is only communicating with that sole device.

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 190 points

    Hi Cynthia,

    Thank you for your answer.

    When I tested these ADC, I was performing the tests on a point-to-point bus with only one master (MCU) and one slave (ADC).
    I checked the voltage on the pins and I didn't saw any irregular values.

    Best regards
    Nuno Dias

    PS: I remind you again that this issue is not very problematic because I can use another address.