RL78/G14
Recommended PCB Layout for Reducing Noise
4. Reducing
Noise
Test
of Different Layout
4.1 Test
Description
In this test, two types of PCB were used. One is designed according to the countermeasures. The other is designed
without the countermeasures. The PCB layouts around the MCU are shown as Figure 3.2. The peripheral circuits on the
two boards are same. Same noise interference is input to the two test boards through the power supply for 1 minute.
The peak value of noise interference steps up in 100 V increments from 100 V to 4000 V in every test.
On the target boards, there are two groups of LEDs that blink to show the MCU status. All LEDs will be ON for 5
seconds after the MCU resets. Then the two groups of LEDs will blink from “0000
2
” to “1111
2
” by “1
2
”. One group is
controlled by the main loop; the other group is controlled by timer interrupt. These two groups of LEDs will blink
synchronously.
The MCU status can be evaluated by observing these LEDs.
•
If the MCU operates normally within 1 minute, the result is considered good and the table is filled with a “ ”.
•
If the MCU generates an abnormal phenomena (reset, program runaway, or LEDs blink asynchronously) within 1
minute, the result is considered not good and the table is filled with a “ ”.
Figure 4.1 shows the diagram of test environment.
AC220V
Isolated
transformer
1 : 1
Noise Generator
AC220V
Source
input
Po
w
e
r
in
put
AC220V
Noise
Out
p
ut
Power supply for
test circuit
Power supply for
noise generator
LEDs
Power
circuit
MCU
DC5V
Figure 4.1 Diagram of Test Environment
4.2 Test
Conditions
•
Test tools:
⎯
Noise generator: NoiseKen INS-4040
⎯
Target board: Recommended board and non-recommended board
•
Test conditions:
⎯
Target board power: 220 V 50 Hz
⎯
MCU type: R5F104LEAFA
⎯
Oscillation frequency: 20 MHz
⎯
MCU power source: 5 V
⎯
MCU bypass capacitor: 0.1
μ
F
⎯
Noise period: 16 ms
⎯
Noise pulse width: 50 ns
⎯
Noise polarity: plus and minus
⎯
Noise peak value: 100 to 4000 V
⎯
Test time: 1 minute
R01AN1876EC0100 Rev. 1.00
Page 9 of 14
Feb. 28, 2014
