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DAC7718: Timing in the power up sequence

Norman Pellet
Prodigy 110 points
Part Number: DAC7718
Other Parts Discussed in Thread: LM3880

Hello,

I'm having trouble to communicate with my DAC7718. It might be totally unrelated to my question, but I just wanted to check this out before moving further.

I've been reading about the importance of power up sequencing.

On my product, the IOVDD and DVDD (=3.3V) are provided by an LDO, which is powered by AVDD (the analog power used on the DAC). So I guess technically IOVDD is applied a few microseconds after AVDD is applied. Is that a problem ? If so, can you recommend a TI part, such as a load switch, that can handle this situation (notably to providing switching for AVSS).

Thanks,

Norman

  • 0
    TI__Genius 14220 points
    Hi Norman,

    According to the datasheet, the power-on sequencing should be implemented as follows:

    "For proper power-on initialization of the device, IOVDD and the digital pins must be applied before or at the same
    time as DVDD. If possible, it is preferred that IOVDD and DVDD can be connected together in order to simplify the
    supply sequencing requirements. Pull-up resistors should go to either supply. AVDD should be applied after the
    digital supplies (IOVDD and DVDD) and digital initialization pins (LDAC, CLR, RST, CS, and RSTSEL). AVSS can
    be applied at the same time as or after AVDD. The REF-x pins must be applied last."

    You can use LM3880 along with power MOSFETs wherever needed to sequence these power supplies. Please note that even the REF should be sequenced. So, it will be good if you sequence (1) IOVDD and DVDD, (2) AVDD and AVSS and (3) REFA and REFB. You can use the 3 enable pins of LM3880 to do this although you don't need a switch for the first case - the main power will do.

    You can also refer to a related post: e2e.ti.com/.../2147632

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs