RL78/G14
Recommended PCB Layout for Reducing Noise
R01AN1876EC0100 Rev. 1.00
Page 4 of 14
Feb. 28, 2014
2. Recommended PCB Layout
Good PCB layout is very important in reducing noise design. Some countermeasures of improving reducing noise
performance are shown below.
2.1
Wiring of VDD and VSS
•
Connect the MCU and main power supply with the shortest possible wiring.
•
Make the VDD and VSS wiring equal in length.
•
Make the wiring for the VDD and VSS wider than other signal wiring.
•
Separate the wiring for the VDD and VSS on the MCU from the wiring for the peripheral function power supply.
And try to separate them at the entrance of the main power supply.
2.2 Oscillator
Concerns
•
Place the oscillator circuit close to the MCU.
•
Connect the MCU and oscillator circuit with the shortest possible wiring.
•
Separate the VSS wiring between the MCU and the oscillator from the VSS wiring for the other peripherals.
2.3 Bypass
Capacitor
•
Place the bypass capacitor between VSS wiring and VDD wiring close to the MCU. And make power supply wiring
connect to the MCU via the bypass capacitor leads.
•
Make the wiring length between the bypass capacitor and VDD pin or VSS pin equal and as short as possible.
2.4
Wiring of RESET Pin
•
Place the reset circuit close to the MCU.
•
Connect the MCU and reset circuit with the shortest possible wiring.
•
Separate the VDD wiring and VSS wiring of reset circuit from the VSS and VDD wiring for the other peripherals.
2.5
Wiring of REGC Pin
•
Connect the REGC pin to VSS via a 0.47 to 1
μ
F (default: 0.47
μ
F) capacitor as the MCU user’s manual
recommends.
•
Place the REGC circuit close to the MCU.
•
Connect the MCU and REGC circuit with the shortest possible wiring.
2.6
Wiring of TOOL0 Pin
•
Connect the TOOL0 pin to VDD via a 1 k
Ω
resistor as the MCU user’s manual recommends.
•
Place the TOOL0 circuit close to the MCU.
•
Connect the MCU and TOOL0 circuit with the shortest possible wiring.
