SMPS
VCC
C2C1
MCU
VDD
R1
C3
VSS
1. The C1 capacitor is to flatten out the voltage of the SMPS power, VCC.
√ Recommended C1: 470uF/25V more.
2. The R1 and C2 are the RC filter for VDD and suppress the ripple of VCC.
√ Recommended R1: 10Ω - 20Ω
√ Recommended C2: 47uF/25V more
√ The R1 and C2 should be as close by the C3 as possible.
3. The C3 capacitor is used for temperature compensation because an electrolytic capacitor
becomes worse characteristics at low temperature.
√ Recommended C3: ceramic capacitor 2.2uF more
√ The C3 should be within 1cm from VDD pin of MCU on the PCB layout.
4. The above circuit is recommended to improve noise immunity (EFT, Surge, ESD, etc) when the
SMPS supplies the VDD of MCU.
SMPS Side MCU Side
Figure 7.16 Recommended Circuit and Layout with SMPS Power
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