AD7891ASZ-1 when supply VDD in digital and analog power supply separately

Hi,all

Our customer will start to design the mixed signal circuits with AD7891ASZ-1.

They are looking into circuits that supply the VDD separately for analog (pin4) and digital (pin13) power supply line.

In the datasheet, from "Power Supply Bypassing and Grounding",

One of the VDD pins (Pin 10 of the PLCC package and Pin 4 on the MQFP package) mainly drives the analog circuitry on the chip.

The other VDD pin (Pin 19 on the PLCC package and Pin 13 on the MQFP package) mainly drives digital circuitry on the chip.

Our question is,

If supply the VDD in digital (pin13) and analog (pin4) power supply line separately w/AD7891ASZ-1,

Is it necessary to consider the power supply sequence? for example analog first, digital next,
or should analog and digital start at the same time?

Best regards,

sss

  • Hi sss,

       The VDD pins are the same function. These pin(VDD) should be power up at the same time, they supply the circuits inside. For power up sequencing the Vdd should be power up first followed by the Reference and digital input voltages. If the power ups sequence is not mentioned in any datasheet, the section to look in the datasheet would be the abs/max rating. It is implicitly shown on the abs/max table.

    Regards,

    Jonathan