AD9882ASLASHPCB datasheet(37/40 Pages) AD

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AD9882A

Rev. 0 | Page 37 of 40

PLL

Place the PLL loop filter components as close to the FILT pin as

possible.

Do not place any digital or other high frequency traces near

these components.

Use the values suggested in the data sheet with 10% or smaller

tolerances.

OUTPUTS: DATA AND CLOCKS

Try to minimize the trace length that the digital outputs have to

drive. Longer traces have higher capacitance and require more

current, which causes more internal digital noise.

Shorter traces reduce the possibility of reflections.

Adding a series resistor with a value of 22 Ω to 100 Ω can

suppress reflections, reduce EMI, and reduce the current spikes

inside of the AD9882A. However, if 50 Ω traces are used on the

PCB, the data output should not need these resistors.

A 22 Ω resistor on the DATACK output should provide good

impedance matching that can reduce reflections. If EMI or

current spiking is a concern, use a lower drive strength setting

by adjusting Register 0x14. If series resistors are used, place

them as close as possible to the AD9882A pins but avoid adding

vias or extra length to the output trace to get the resistors closer.

If possible, limit the capacitance that each of the digital outputs

drives to less than 10 pF by keeping traces short and connecting

the outputs to only one device. Loading the outputs with

excessive capacitance increases the current transients inside the

AD9882A, creating more digital noise on its power supplies.

DIGITAL INPUTS

The digital inputs on the AD9882A were designed to work with

3.3 V signals, but are tolerant of 5.0 V signals. No extra

components need to be added, if 5.0 V logic is used.

Any noise that gets onto the Hsync input trace adds jitter to the

system. Therefore, minimize the trace length and do not run

any digital or other high frequency traces near it.

VOLTAGE REFERENCE

Bypass with a 0.1 µF capacitor. Place as close as possible to the

AD9882A pin. Make the ground connection as short as

possible.

AD9882A/PCB データシート(PDF) 37 Page - Analog Devices

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