RL78/G14
Recommended PCB Layout for Reducing Noise
5.2
Test Results of the Modified Board
Table 5.1 Test Results of Non-recommended Board Improvement
Non-recommended
Layout
After Modification
Before Modification
+
−
+
−
4000
(2)
(3)
3900
(2)
(3)
3800
(2)
(3)
3700
(3)
(3)
3600
(3)
(3)
3500
(3)
(3)
3400
(3)
(3)
3300
(3)
(3)
3200
(3)
(3)
3100
(3)
(3)
3000
(3)
(3)
2900
(3)
(3)
2800
(3)
(3)
2700
(3)
(3)
2600
(3)
(3)
2500
(3)
(3)
2400
(3)
2300
(3)
2200
2100
2000
Polarity
Voltage
Note:
Voltage: Noise Value (Unit: V, Higher value shows higher reducing noise capability)
Polarity: Noise polarity added to target board power source
: Normal MCU operation
(1): Reset can not be released; (2): Reset
→
Rerun
→
Reset; (3): Main loop error or runaway
5.3
Recommendations for PCB Board Improvement
After modifications are made on the non-recommended board, the results of reducing noise performance improved
drastically. But when developing a product, the PCB should be redesigned according to the recommended layout.
Note the following precautions for designing the PCB layout
.
•
VDD and VSS: Separate the MCU VDD and VSS wiring from peripherals’ VDD and VSS wiring. Connect to the
main power supply after the filter capacitors.
•
Oscillator concerns: Use the shortest possible wiring to connect the oscillator, capacitor and MCU. Separate
oscillator’s VSS from other peripherals’ VSS wiring.
•
Bypass capacitor: Place the bypass capacitor as close to the MCU as possible. Make sure the leads of the bypass
capacitor are set on the VDD and VSS trunk wiring.
•
Reset circuit: Use the shortest wiring pattern to connect resistor, capacitor and diode.
•
REGC and TOOL0: Place the capacitor and resistor as close to the MCU as possible.
R01AN1876EC0100 Rev. 1.00
Page 13 of 14
Feb. 28, 2014
