ISO6720_V02 datasheet(33/49 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 Section 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/in2.

• 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 at less than 150 Mbps, (or rise and fall times greater than 1 ns), and trace

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

alternatives because of lower dielectric losses at high frequencies, less moisture absorption, greater strength

and stiffness, and the self-extinguishing flammability-characteristics.

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ISO6720, ISO6721, ISO6721R

SLLSFJ0D – JANUARY 2020 – REVISED SEPTEMBER 2021

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ISO6720 Datasheet(PDF) 33 Page - Texas Instruments