Rainbow-electronics DS1080L Bedienungsanleitung PDF herunterladen (Seite 7)

DS1080L

Spread-Spectrum Crystal Multiplier

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Applications Information

Crystal Selection

The DS1080L requires a parallel resonating crystal

operating in the fundamental mode, with an ESR of less

than 90Ω. The crystal should be placed very close to

the device to minimize excessive loading due to para-

sitic capacitances.

Oscillator Input

When driving the DS1080L using an external oscillator

clock, consider the input (X1) to be high impedance.

Crystal Capacitor Selection

The load capacitors C

and C

are selected based

on the crystal specifications (from the data sheet of the

crystal used). The crystal parallel load capacitance is

calculated as follows:

For the DS1080L use C

= C

In this case, the equation then reduces to:

where C

= C

LX.

Equation 2 is used to calculate the values of C

and

based on values on C

and C

noted in the data

sheet electrical specifications.

Power-Supply Decoupling

To achieve best results, it is highly recommended that

a decoupling capacitor is used on the IC power-supply

pins. Typical values of decoupling capacitors are

0.001µF and 0.1µF. Use a high-quality, ceramic, sur-

face-mount capacitor, and mount it as close as possi-

ble to the V

and GND pins of the IC to minimize lead

inductance.

Layout Considerations

As noted earlier, the crystal should be placed very

close to the device to minimize excessive loading due

to parasitic capacitances. Care should also be taken to

minimize loading on pins that could be floated as a pro-

gramming option (SMSEL and CMSEL). Coupling on

inputs due to clocks should be minimized.

Equation

CxC

Equation

DS1080L

NOTE: IN THE ABOVE CONFIGURATION WITH PDN CONNECTED TO V

, SMSEL CONNECTED TO GND

AND CMSEL FLOATING, THE DEVICE IS IN NORMAL OPERATION WITH 2x CLOCK MULTIPLICATION, AND

SPREAD-SPECTRUM MAGNITUDE OF ±0.5%.

SSO

PDN

CRYSTAL

DECOUPLING

CAPACITOR

GND

CMSEL

SMSEL

Typical Operating Circuit

1 2 3 4 5 6 7 8

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