Recommendation for Hardware Setup 32-Bit FR81S Family
Document No. 002-09375 Rev. *B
8
3 Layout and Electromagnetic Compatibility
This chapter gives some tips for layout design.
3.1
General
To avoid ESD problems and noise emission of the system some rules for the layout design have to be observed.
The most critical point is the C pin because this is the connection to the internal 1.2 V supply for the MCU core. Thus,
two decoupling capacitors have to be placed very near to this pin.
Also, the ground and Vcc routing has to be done carefully. Vcc lines should be routed in star shape. We recommend a
Vss ground plane on the mounting side just under the MCU. For both Vcc and Vss only one connection to the rest of
the circuit should be done, otherwise noise is carried-over from and to the MCU. This one connection should be used
for power supply filtering (PI-Filter with ferrite). Decoupling capacitors (DeCaps) have to be placed as near as possible
to the related pins. If they are placed too far away, their functionality becomes useless.
If possible all decoupling capacitors should be placed on the same mounting side as the MCU; otherwise the DeCaps
could be placed on bottom layer below the MCU.
PI-Filter prevents EMI from radiating from power supply planes. Keep maximum distance between IN and OUT
capacitor to avoid noise coupling at PI-Filter.
If crystals are used, they have to be placed as near as possible to the X1(A) pins, output of the inverter. The feedback
resistor of oscillator circuit (typ. 1Mohm) is already implemented internally. The evaluation of crystal/resonator and load
capacitor must be tested by the related crystal vendor by crystal matching test.
3.2
Power supply Pins
The following table shows the EMC critical pins and gives short information about how to connect them.
Table 5. Power Supply pins in use
Pin Name
Function
VCC
Dedicated power supply pins for IO buffer and crystal oscillator.
VCC5*
*Only for CY91570/590 series.
Dedicated power supply pins for IO buffer and crystal oscillator.
VCC3*
*Only for CY91590 series.
Power supply pins for 3V3 IO buffer.
VCCE*
*Only for CY91570 series.
Power supply pins for 3V3 IO buffer.
DVCC*, DVSS*
*Only for CY91570/590 series.
Power supply pins for high current output buffer pins.
VSS
Dedicated power supply (0 V) pins. (IO buffer, MCU core and crystal oscillator)
AVCCn
Dedicated power supply pins for the AD-converter (unit n).
AVRHn / AVRLn
Dedicated positive/negative reference voltage pin for the AD-converter (unit n).
AVSSn
Dedicated power supply pin (0 V) for the AD-converter (unit n).
C
Dedicated power supply pin for the internal power supply regulator (used to supply the
MCU core). External capacitor connected to this pin is required.
C_1*, C_2*, C_3*
*Only for CY91590 series.
Dedicated power supply pins for the internal power supply regulator (used to supply the
MCU core). External capacitors connected to these pins are required. Please refer to
datasheet “C Pin Connection Diagram” reference for further information.
