ISO6741 datasheet(34/46 Pages) TI

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11 Layout

11.1 Layout Guidelines

A minimum of two layers is required to accomplish a cost optimized and low EMI PCB design. To further improve

EMI, a four layer board can be used (see Figure 11-2). Layer stacking for a four layer board should be in the

following order (top-to-bottom): high-speed signal layer, ground plane, power plane and low-frequency signal

layer.

• Routing the high-speed traces on the top layer avoids the use of vias (and the introduction of their

inductances) and allows for clean interconnects between the isolator and the transmitter and receiver circuits

of the data link.

• Placing a solid ground plane next to the high-speed signal layer establishes controlled impedance for

transmission line interconnects and provides an excellent low-inductance path for the return current flow.

• Placing the power plane next to the ground plane creates additional high-frequency bypass capacitance of

approximately 100 pF/inch2.

• Routing the slower speed control signals on the bottom layer allows for greater flexibility as these signal links

usually have margin to tolerate discontinuities such as vias.

If an additional supply voltage plane or signal layer is needed, add a second power or ground plane system to

the stack to keep it symmetrical. This makes the stack mechanically stable and prevents it from warping. Also

the power and ground plane of each power system can be placed closer together, thus increasing the high-

frequency bypass capacitance significantly.

For detailed layout recommendations, refer to the Digital Isolator Design Guide.

11.1.1 PCB Material

For digital circuit boards operating below 150 Mbps, (or rise and fall times higher than 1 ns), and trace lengths of

up to 10 inches, use standard FR-4 UL94V-0 printed circuit boards. This PCB is preferred over cheaper

alternatives due to its lower dielectric losses at high frequencies, less moisture absorption, greater strength and

stiffness, and self-extinguishing flammability-characteristics.

ISO6740-Q1, ISO6741-Q1, ISO6742-Q1

SLLSFG4A – AUGUST 2020 – REVISED JANUARY 2021

www.ti.com

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Product Folder Links: ISO6740-Q1 ISO6741-Q1 ISO6742-Q1

ISO6741 Datasheet(PDF) 34 Page - Texas Instruments