ICS843156 datasheet(9/21 Pages) RENESAS

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ICS843156AK REVISION B May 26, 2016

ICS843156 Data Sheet

CRYSTAL-TO-LVPECL CLOCK SYNTHESIZER

Applications Information

Recommendations for Unused Input and Output Pins

Inputs:

TEST_CLK Input

For applications not requiring the use of the test clock, it can be left

floating. Though not required, but for additional protection, a 1k



resistor can be tied from the TEST_CLK to ground.

Crystal Inputs

For applications not requiring the use of the crystal oscillator input,

both XTAL_IN and XTAL_OUT can be left floating. Though not

required, but for additional protection, a 1k

 resistor can be tied from

XTAL_IN to ground.

LVCMOS Control Pins

All control pins have internal pulldowns; additional resistance is not

required but can be added for additional protection. A 1k

 resistor

can be used.

Outputs:

LVPECL Outputs

All unused LVPECL outputs can be left floating. We recommend that

there is no trace attached. Both sides of the differential output pair

should either be left floating or terminated.

Power Supply Filtering Technique

As in any high speed analog circuitry, the power supply pins are

vulnerable to random noise. To achieve optimum jitter perform ance,

power supply isolation is required. The ICS843156 provides separate

power supplies to isolate any high switching noise from the outputs

to the internal PLL. VCC, VCCA and VCCO should be individually

connected to the power supply plane through vias, and 0.01µF

bypass capacitors should be used for each pin. Figure 1 illustrates

this for a generic VCC pin and also shows that VCCA requires that an

additional 10

 resistor along with a 10F bypass capacitor be

connected to the VCCA pin.

Figure 1. Power Supply Filtering

Crystal Input Interface

The ICS843156 has been characterized with 18pF parallel resonant

crystals. The capacitor values, C1 and C2, shown in Figure 2 below

were determined using a 25MHz, 18pF parallel resonant crystal and

were chosen to minimize the ppm error. The optimum C1 and C2

values can be slightly adjusted for different board layouts.

Figure 2. Crystal Input Interface

VCC

VCCA

3.3V

10µF

0.01µF

XTAL_IN

XTAL_OUT

18pF Parallel Crystal

27pF

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