AD9558BCPZ datasheet(60/105 Pages) AD

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AD9558

Data Sheet

Rev. C | Page 60 of 105

POWER SUPPLY PARTITIONS

The AD9558 power supplies are divided into four groups:

DVDD3, DVDD, AVDD3, and AVDD. All power and ground

pins must be connected, even if certain blocks of the chip are

powered down.

This section recommends the use of ferrite beads. Most users

report that the use of bypass capacitors together with ferrite

beads is the best arrangement, although some have reported

that ferrite beads alone are superior.

RECOMMENDED CONFIGURATION FOR 3.3 V

SWITCHING SUPPLY

A popular power supply arrangement is to power the AD9558

with the output of a 3.3 V switching power supply.

When the AD9558 is powered using 3.3 V switching power

supplies, all of the 3.3 V supplies can be connected to the 3.3 V

switcher output, and a 0.1 µF bypass capacitor must be placed

adjacent to each 3.3 V power supply pin.

Use of Ferrite Beads on 3.3 V Supplies

To ensure the best output to output isolation when using the

3.3 V CMOS output driver mode, use one ferrite bead each for

Pin 25 and Pin 26. However, a ferrite bead is not needed if 3.3 V

output driver mode is not used. However, the 3.3 V power supply

must still be connected to these pins even if the mode is not used.

CONFIGURATION FOR 1.8 V SUPPLY

When 1.8 V supplies are preferred, it is recommended that an

LDO regulator, such as the ADP222, be used to generate the

1.8 V supply from the 3.3 V supply.

The ADP222 offers excellent power supply rejection in a small

(2 mm × 2 mm) package. It has two 1.8 V outputs. One output

can be used for the DVDD pins (Pin 6, Pin 34, and Pin 35), and

the other output can drive the AVDD pins.

The ADP7104 is another good choice for converting 3.3 V to

1.8 V. The close-in noise of the ADP7104 is lower than that of

the ADP222; therefore, it may be better suited for applications

where close-in phase noise is critical and the AD9558 DPLL

loop bandwidth is <50 Hz. In such cases, all 1.8 V supplies can be

connected to one ADP7104.

Use of Ferrite Beads on 1.8 V Supplies

To ensure the best output-to-output isolation, use one ferrite

bead for each of the following AVDD pins: Pin 12, Pin 17,

Pin 22, Pin 29, and Pin 30. The ferrite beads must be placed in

between the 1.8 V LDO output and each pin listed previously.

Ferrite beads that have low (<0.7 Ω) dc resistance and

approximately 600 Ω impedance at 100 MHz are suitable for

this application.

Pin 6 and Pin 56 are 1.8 V digital supplies, and while they are

not susceptible to external noise, they are themselves a source of

digital noise. Therefore, a ferrite bead is recommended for each

of these pins. Pin 55 and Pin 56 can be joined together.

See Table 2 for the current consumed by each group. See

Figure 20, Figure 21, and Figure 22 for information on the

power consumption vs. output frequency.

AD9558BCPZ Datasheet(PDF) 60 Page - Analog Devices

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