ada4927 Analog Devices, Inc., ada4927 Datasheet - Page 22

• Manufacturer Part Number: ada4927
• Description: Ultralow Distortion Current Feedback Differential Adc Driver
• Manufacturer: Analog Devices, Inc.

ADA4927-1/ADA4927-2
LAYOUT, GROUNDING, AND BYPASSING
As a high speed device, the ADA4927 is sensitive to the PCB
environment in which it operates. Realizing its superior performance
requires attention to the details of high speed PCB design. This
section shows a detailed example of how the ADA4927-1 was
addressed.
The first requirement is a solid ground plane that covers as
much of the board area around the ADA4927-1 as possible.
However, clear the area near the feedback resistors (RF), gain
resistors (RG), and the input summing nodes (Pin 2 and Pin 3) of
all ground and power planes (see Figure 55). Clearing the ground
and power planes minimizes any stray capacitance at these nodes
and prevents peaking of the response of the amplifier at high
frequencies. Whereas ideal current feedback amplifiers are
insensitive to summing node capacitance, real-world amplifiers
can exhibit peaking due to excessive summing node capacitance.
The thermal resistance, θ
the exposed pad, soldered to a high thermal conductivity 4-layer
circuit board, as described in EIA/JESD 51-7.
Figure 55. Ground and Power Plane Voiding in Vicinity of RF AND RG
Figure 57. Cross-Section of 4-Layer PCB Showing Thermal Via Connection to Buried Ground Plane (Dimensions in Millimeters)
JA
, is specified for the device, including
GROUND PLANE
BOTTOM METAL
POWER PLANE
TOP METAL
Rev. 0 | Page 22 of 24
VIA HOLE
PLATED
1.30
0.30
Bypassed 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. The
1000 pF capacitor should be placed closer to the device. Further
away, provide low frequency bulk bypassing, using 10 μF
tantalum capacitors from each supply to ground.
Make signal routing 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, place PCB traces close
together, and twist any differential wiring such that the loop
area is minimized. Doing this reduces radiated energy and
makes the circuit less susceptible to interference.
Figure 56. Recommended PCB Thermal Attach Pad Dimensions (Millimeters)
1.30
0.80
1.30
0.80