Triple PLL Field Programmable SS VersaClock Synthesizer

MDS 345 D

4

Revision 090704

Integrated Circuit Systems, Inc.

ICS345

frequencies; thus, lowering a system’s electromagnetic

interference (EMI). The modulation rate is the time from

transitioning from a minimum frequency to a maximum

frequency and then back to the minimum.

Spread Spectrum Modulation can be applied as either

“center spread” or “down spread”. During center spread

modulation, the deviation from the target frequency is

equal in the positive and negative directions. The

effective average frequency is equal to the target

frequency. In applications where the clock is driving a

component with a maximum frequency rating, down

spread should be applied. In this case, the maximum

frequency, including modulation, is the target

frequency. The effective average frequency is less than

the target frequency.

The ICS345 operates in both center spread and down

spread modes. For center spread, the frequency can

be modulated between +/- 0.125% to +/-2.0%. For

down spread, the frequency can be modulated

between -0.25% to -4.0%.

Both output frequency banks will utilize identical spread

spectrum percentage deviations and modulation rates,

if a common VCO frequency can be identified.

Spread Spectrum Modulation Rate

The spread spectrum modulation frequency applied to

the output clock frequency may occur at a variety of

rates. For applications requiring the driving of

“down-circuit” PLLs, Zero Delay Buffers, or those

adhering to PCI standards, the spread spectrum

modulation rate should be set to 30-33 kHz. For other

applications, a 120 kHz modulation option is available.

Absolute Maximum Ratings

Stresses above the ratings listed below can cause permanent damage to the ICS345. These ratings, which

are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of the

device at these or any other conditions above those indicated in the operational sections of the

specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can

affect product reliability. Electrical parameters are guaranteed only over the recommended operating

temperature range.

Parameter

Condition

Min.

Typ.

Max.

Units

Supply Voltage, VDD

Referenced to GND

7

V

Inputs

Referenced to GND

-0.5

VDD+0.5

V

Clock Outputs

Referenced to GND

-0.5

VDD+0.5

V

Storage Temperature

-65

150

°C

Soldering Temperature

Max 10 seconds

260

°C

Junction Temperature

125

°C