AD9572

Rev. 0 | Page 14 of 20

THEORY OF OPERATION

REFSEL

XTAL

OSC

REFCLK

VS

VS

BYPASS1

GND

1

0

AD9572

DIVIDE

BY 5

DIVIDE

BY 4

DIVIDE

BY 5

DIVIDE

BY 3

33M

FORCE_LOW

CMOS

33.33MHz

0

1

1

0

125MHz/100MHz

LVPECL/

LVDS

100M/125M

100M/125M

100M/125M

100M/125M

125MHz/100MHz

LVPECL/

LVDS

25M

CMOS

LDO

PHASE

FREQUENCY

DETECTOR

CHARGE

PUMP

DIVIDE

BY 17

DIVIDE

BY 5

DIVIDE

BY 4

VCO

106M

106M

LVPECL/

LVDS

106.25MHz

106M

106M

LDO

PHASE

FREQUENCY

DETECTOR

CHARGE

PUMP

DIVIDE

BY 25

DIVIDE

BY 4

DIVIDE

BY 4

VCO

156M

156M

156.25MHz

LVPECL/

LVDS

BYPASS2

LEVEL

DECODE

FREQSEL

Figure 12. Detailed Block Diagram

Figure 12 shows a block diagram of the AD9572. The chip

combines dual PLL cores, which are configured to generate the

specific clock frequencies required for networking applications,

without any user programming. This PLL is based on proven

Analog Devices synthesizer technology, noted for its exceptional

phase noise performance. The AD9572 is highly integrated and

includes loop filters, regulators for supply noise immunity, all

the necessary dividers with multiple output buffers in a choice

of formats, and a crystal oscillator. A user need only supply a

25 MHz reference clock or an external crystal to implement an

entire line card clocking solution

that does not require any processor intervention. A copy of

the 25 MHz reference source is also available.

OUTPUTS

Table 14 provides a summary of the outputs available.

Table 14. Output Formats

Frequency

Format

Copies

25 MHz

CMOS

1

106.25 MHz

LVPECL/LVDS

2

156.25 MHz

LVPECL/LVDS

1

100 MHz or 125 MHz

LVPECL/LVDS

2

33.33 MHz

CMOS

1

Note that the pins labeled 100M/125M can provide 100 MHz or

125 MHz by strapping the FREQSEL pin as shown in Table 15.