The layout example in this section shows
the recommended placement for decoupling capacitors and ESD protection diodes. A continuous
ground plane is recommended below the D+/D- signal traces. Small footprint capacitors
(0402/0201) are recommended so that these can be placed very close to the supply pins and
corresponding ground pins and connected using the top layer. There must not be any vias in
the routing path between the decoupling capacitors and the corresponding supply and ground
pins. The capacitors on V1P8Vx supplies are
higher in priority when considering placement close to the IC. The ESD protection
diodes must be placed close to the connector with a strong connection to the ground plane.
Pins 4 and 11 for V1P8V1 and pins 18 and 25
for V1P8V2 are connected together, but this connection is after the decoupling
capacitors. If more than two layers are available in the PCB, this connection must be made
in an inner or bottom layer (for example, Layer 3 or 4) to not interrupt the ground plane
under the D+/D- traces. The example shown is for an isolated host or hub, but similar
considerations apply for isolated peripherals as well. The 120μF capacitor on VBUS only
applies to host or hub and must not be used for peripherals. A ferrite bead, with dc
resistance less than 100mΩ, can be optionally placed on the VBUS route, after the 100nF (and
120μF) capacitors to prevent transients such as ESD from affecting the rest of the circuits.
For best performance, minimize the
length of D+/D- board traces from the MCU to ISOUSB211-Q1, and from ISOUSB211-Q1 to the connector. Vias and stubs on D+/D- lines must be avoided. This is especially important for High Speed
Operation.
Connect a small plane (for example, 2mm × 2mm) to the GND
pins on the top layer to improve thermal performance. Connect this to the ground player in
the second layer with multiple vias.