Data Sheet

ADA4950-1/ADA4950-2

Rev. B | Page 23 of 26

LAYOUT, GROUNDING, AND BYPASSING

As a high speed device, the ADA4950-x is sensitive to the

PCB environment in which it operates. Realizing its superior

performance requires attention to the details of high speed

PCB design.

The first requirement is a solid ground plane that covers as

much of the board area around the ADA4950-x as possible. The

thermal resistance, θJA, is specified for the device, including the

exposed pad, soldered to a high thermal conductivity 4-layer

circuit board, as described in EIA/JESD51-7.

Bypass the power supply pins as close to the device as possible

and directly to a nearby ground plane. Use high frequency

ceramic chip capacitors. It is recommended that two parallel

bypass capacitors (1000 pF and 0.1 μF) be used for each supply.

Place the 1000 pF capacitor closer to the device. Farther away,

provide low frequency bulk bypassing using 10 μF tantalum

capacitors from each supply to ground.

Signal routing should be short and direct to avoid parasitic

effects. Wherever complementary signals exist, provide a

symmetrical layout to maximize balanced performance. When

routing differential signals over a long distance, keep PCB

traces close together, and twist any differential wiring to

minimize loop area. Doing this reduces radiated energy and

makes the circuit less susceptible to interference.

1.30

0.80

0.80

1.30

Figure 61. Recommended PCB Thermal Attach Pad (Dimensions in Millimeters)

0.30

PLATED

VIA HOLE

1.30

GROUND PLANE

POWER PLANE

BOTTOM METAL

TOP METAL

Figure 62. Cross-Section of 4-Layer PCB Showing Thermal Via Connection to Buried Ground Plane (Dimensions in Millimeters)