8431AM-21

www.icst.com/products/hiperclocks.html

REV. A APRIL 27, 2005

1

Integrated

Circuit

Systems, Inc.

ICS8431-21

TO

The ICS8431-21 is a general purpose clock fre-

quency synthesizer for IA64/32 application and a

member of the HiPerClockS™ family of High Per-

formance Clock Solutions from ICS. The VCO op-

erates at a frequency range of 250MHz to 700MHz

providing an output frequency range of 62.5MHz to 350MHz.

The output frequency can be programmed using the parallel in-

terface, M0 through M8 to the configuration logic, and the output

divider control pin, DIV_SEL. Spread spectrum clocking is pro-

grammed via the control inputs SSC_CTL0 and SSC_CTL1.

Programmable features of the ICS8431-21 support four op-

erational modes. The four modes are spread spectrum clock-

ing (SSC), non-spread spectrum clock and two test modes

which are controlled by the SSC_CTL[1:0] pins. Unlike other

synthesizers, the ICS8431-21 can immediately change

spread-spectrum operation without having to reset the device.

In SSC mode, the output clock is modulated in order to achieve

a reduction in EMI. In one of the PLL bypass test modes, the

PLL is disconnected as the source to the differential output

allowing an external source to be connected to the TEST_I/O

pin. This is useful for in-circuit testing and allows the differen-

tial output to be driven at a lower frequency throughout the

system clock tree. In the other PLL bypass mode, the oscilla-

tor divider is used as the source to both the M and the Fout

divide by 2. This is useful for characterizing the oscillator and

internal dividers.

XTAL_IN

XTAL_OUT

M0:M8

PLL

FOUT

nFOUT

÷ 16

TEST_I/O

OSC

VCO

÷2

÷4

PHASE

DETECTOR

÷ M

SSC

Control

Logic

Configuration

Logic

nP_LOAD

SSC_CTL0

• Fully integrated PLL

• Differential 3.3V LVPECL output

• Crystal oscillator interface

• Output frequency range: 62.5MHz to 350MHz

• Crystal input frequency range: 14MHz to 25MHz

• VCO range: 250MHz to 700MHz

• Programmable PLL loop divider for generating a variety

of output frequencies

• Spread Spectrum Clocking (SSC) fixed at 1/2% modulation

for environments requiring ultra low EMI

• PLL bypass modes supporting in-circuit testing and on-chip

functional block characterization

• Cycle-to-cycle jitter: 30ps (maximum)

• 3.3V supply voltage

• 0°C to 85°C ambient operating temperature

• Replaces ICS8431-01 and ICS8431-11

• Lead-Free package fully RoHS compliant

SSC_CTL1

M0

M1

M2

M3

M4

M5

M6

M7

M8

SSC_CTL0

SSC_CTL1

TEST_I/O

1

2

3

4

5

6

7

8

9

10

11

12

13

14

28

27

26

25

24

23

22

21

20

19

18

17

16

15

nP_LOAD

XTAL_IN

XTAL_OUT

nc

nc

MR

DIV_SEL

FOUT

nFOUT

ICS8431-21

28-Lead SOIC

7.5mm x 18.05mm x 2.25mm package body

M Package

Top View

DIV_SEL

HiPerClockS™

ICS