Setting the Output Voltage
The internal reference VREF is 0.6V (Typical).The
output voltage is divided by a resistor divider,R1 and
R2 to the FB pin. The output voltage is given by
(1 +R1/R2)*Vref=Vout
Inductor Selection
The recommended values of inductor are 4.7 to
22μH. Small size and better efficiency are the major
concerns for portable device, such as MT3608 used
for mobile phone. The inductor should have low core
loss at 1.2MHz and low DCR for better efficiency. To
avoid inductor saturation current rating should be
considered.
Capacitor Selection
Input and output ceramic capacitors of 22μF are
recommended for MT3608 applications. For better
voltage filtering, ceramic capacitors with low ESR
are recommended. X5R and X7R types are suitable
because of their wider voltage and temperature
ranges.
Diode Selection
Schottky diode is a good choice for MT3608
because of its low forward voltage drop and fast
reverses recovery. Using Schottky diode can get
better efficiency. The high speed rectification is also
a good characteristic of Schottky diode for high
switching frequency. Current rating of the diode must
meet the root mean square of the peak current and
output average current multiplication as following :
I D (RMS) ≈ I OUT × I PEAK
The diode’ s reverse breakdown voltage should be
larger than the output voltage.
以下是布局的要求：
Layout Consideration
For best performance of the MT3608, the following
guidelines must be strictly followed.
Input and Output capacitors should be placed
close to the IC and connected to ground plane
to reduce noise coupling.
The GND should be connected to a strong
ground plane for heat sinking and noise
protection.
Keep the main current traces as possible as
short and wide.
SW node of DC-DC converter is with high
frequency voltage swing. It should be kept at a
small area.
Place the feedback components as close as
possible to the IC and keep away from the
noisy devices.
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