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AD9549

Preliminary Technical Data

Rev. PrA | Page 52 of 78

POWER MANAGEMENT

The AD9549 features multiple power supplies, and their power

consumption varies with its configuration. This section covers

which power supplies can be grouped together, and how each

block’s power consumption varies with frequency.

The numbers quoted here are for comparison only. Please refer

to the spec table for exact numbers. With each group, bypass

caps of 1 uF in parallel with a 10 uF should be used.

The recommendations here are for typical applications, and an

application demanding the highest performance may require

additional power supply isolation.

3.3V SUPPLIES

Digital I/O (Pin 1) and VDDX_REF (Pin 14): These two 3.3V

supplies can be grouped together. The power consumption on

Pin 1 varies dynamically with serial port activity. Noise from

the serial port that couples into the reference input should be

filtered by the digital PLL.

AVDD3 (Pin 37): This is the CMOS driver supply. If the CMOS

driver will be used, this supply should be isolated from other

3.3V supplies to avoid a spur at the output frequency. The

power consumption is a function of the output frequency and

loading of this pin. If this supply will not be used, this supply

can be tied to other 3.3V supplies, and its consumption will be

less than 5 mA.

AVDD3 (Pins 46,47,49): These are 3.3V DAC power supplies

that typically consume about 25mA. At a minimum, a ferrite

bead should be used to isolate these from other 3.3V supplies,

with a separate regulator being ideal.

1.8V SUPPLIES

Digital Core (Pins 3,5,7): These Pins can be grouped together.

Their current consumption increases from about 160mA at a

system clock of 700 MHz to about 220mA a system clock of 1

GHz. There is also a slight (~5%) increase as Fout increases

from 50 MHz to 400 MHz.

VDD DAC Decoder (Pin 53): This 1.8V supply consumes about

20 to 40 mA. It is critical that this supply be well isolated from

other 1.8V supplies. At a minimum, a ferrite bead should be

used for isolation, with a separate regulator being ideal.

AVDD (Pins 11, 19, 23, 24, 36, 42, 45): These pins may be

grouped together and should be isolated from other 1.8V

supplies. At a minimum, a ferrite bead should be used for

isolation, with a separate regulator being ideal.

AVDD (Pin 25, 26, 29, 30): These pins may be grouped together

and should be isolated from other 1.8V supplies. At a

minimum, a ferrite bead should be used for isolation, with a

separate regulator being ideal.

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