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DAC8775: Doubts on DVDD supply for DAC8775 chip

Naveen kumar
Prodigy 65 points
Part Number: DAC8775
Other Parts Discussed in Thread: , ISO7720

Hello Team,

         I'm working with DAC8775. I have doubts on DVDD supply to DAC8775 chip. What will happen if DVDD is supplied by both Internal DVDD(LDO) of the chip

and as well as through the external power supply. In hardware design DVDD_EN pin( pin 66 of DAC8775 chip ) is left floating as well as the DVDD pin (pin 66 of DAC) is fed with +5v?

      1. Will it damage the chip on newly designed board?

      2. Will it have any impact on SPI communication? - Now I wasn't able to establish SPI communication with newly designed board which wasn't the case with DAC8775EVM board.

Thanks,

Naveen

  • 0
    TI__Guru* 92785 points

    Naveen,


    If the DVDD_EN pin is left floating, the DVDD is powered through an internal LDO. I believe the DVDD_EN has an internal pull-up to enable DVDD. If you attach and external supply to DVDD, you are attaching power to the output of the LDO and it is certainly possible to damage the device. If this is the case, then you might you might lose communications with the device.

    I would still check to make sure the connections are all correct, but it is certainly possible the communication loss is due to damage. When the device is first powered up, without the DVDD contention, how much current is being drawn by the device? My recollection is that the device draws about 3mA when first powered up.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 65 points

    Hi joseph, 

             It seems that hardware team designed board such that they're using Internal LDO to power up the chip( for DVDD ) by keeping DVDD_EN pin floating.

    They also say that they're using pin 66 DVDD pin to supply to other components of the chips like Digital Isolator (ISO7720). From the datasheet I see that it 

    pin 66 can be used as Input/Output. At which condition DVDD pin (66) will work as Output?

    Thanks,

    Naveen

  • +1 in reply to Naveen kumar
    TI__Guru* 92785 points

    Naveen,


    If the DVDD is enabled, the pin should automatically output the LDO voltage of approximately 5V. With the DVDD_EN floating, that should enable the LDO and you should be able to measure the 5V on the pin.

    I would note that the current is limited to 10mA and the load capacitance is maximum is only about 200pF.


    Joseph Wu