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AMC7812 IOVDD with respect to other supplies

Ted Ustun
Prodigy 20 points
Other Parts Discussed in Thread: AMC7812

What is the requirement for the IOVDD with respect to other supplies on-chip? While the AMC7812 datasheet outlines the preferred way of powering up the device - it does not tell voltage supply absolute maximum with respect to each other (not to ground).

Thx, Ted

  • 0
    TI__Genius 11750 points

    Hello Ted,

    Welcome to the E2E forums.  As you may have noticed the datasheet specifies that there is no required sequence, as the supplies can be brought up independently.  But it is important to note that the device must receive a hardware reset prior to any communication to the device, this hardware reset will ensure that the device enters specified operation.  This information is found on page 49 of the DS.  

    Additionally, to avoid activating the ESD protection diodes of the AMC7812, the GPIO inputs should not be applied before the AVDD supply is established.  Also, if using the external reference configuration of the ADC, ADC-REF-IN/CMP should not be applied before AVDD.

    As long as the above is followed, and absolute maximums of the supply pins are not violated the part will enter correct operation.

    Best Regards,

    Matt

  • 0 in reply to Matthew Sauceda
    Prodigy 20 points

    Dear Matt - thx for the quick response. I'm experiencing some issues with communicating the AMC7812 on our custom board. I've tried both I2C and SPI with no luck. At this point I'd like to rule out the possibility of having a dead IC on my board. My question is - should I expect to see Vref at Pin 57 (Ref-Out)? At this point it reads 0V (Zero). BTW - I applied the reset per your guidance/datasheet. You feedback is appreciated.

    Regards,

    Ted

  • 0 in reply to Ted Ustun
    TI__Genius 11750 points

    Hello Ted,

    To enable the internal reference you must set the PREF bit in the Powerdown Register.  This register also includes the power on bits for the ADC and DAC channels.  Once the PREF bit is set to '1', the Ref-Out pin will output 2.5V.  This information is included in page 39 of the DS.  

    Regarding the SPI/I2C communication, can you supply any oscilloscope captures of the communication with the AMC7812 device?  This information will help rule out any communication error from the host controller.  A schematic with the device will also be helpful for debug.

    Best Regards,

    Matt