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©2023 Renesas Electronics Corporation

January 31, 2023

841608 Datasheet

Applications Information

Recommendations for Unused Input and Output Pins

Inputs:

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.

REF_IN Input

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

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

resistor can be tied from the REF_IN to ground.

Outputs:

HCSL Outputs

All unused HCSL 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

performance, power supply isolation is required. The 841608

provides separate power supplies to isolate any high switch-

ing noise from the outputs to the internal PLL. VDD and VDDA

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 VDD pin and

also shows that VDDA requires that an additional 10 resistor

along with a 10µF bypass capacitor be connected to the

VDDA pin.

Figure 1. Power Supply Filtering

VDD

VDDA

2.5V

10

10µF

.01µF

.01µF