EV3406DS-00A 데이터 시트보기 (PDF) - Monolithic Power Systems
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EV3406DS-00A Datasheet PDF : 8 Pages
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TM
BLOCK DIAGRAM
IN 2
EN 7
7.0V
INTERNAL
REGULATORS
5V
OSCILLATOR
SLOPE
COMP
130/210KHz
CLK
+
1.0V --
--
SHUTDOWN
COMPARATOR
LOCKOUT
COMPARATOR
2.30V/
2.50V
+
+
--
CURRENT
SENSE
AMPLIFIER
+
--
5V
+
SQ
RQ
--
CURRENT
COMPARATOR
1.8V
FREQUENCY
FOLDBACK
COMPARATOR
-- 0.7V 1.23V + ERROR
AMPLIFIER
5 FB
6 COMP
1 BS
M1
3 SW
M2
4 GND
CM3406_BD01
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive voltage
divider from the output voltage to FB pin. The
voltage divider divides the output voltage down to
the feedback voltage by the ratio:
VFB
=
VOUT
R2
R1+ R2
Where VFB is the feedback voltage and VOUT is the
output voltage.
Thus the output voltage is:
VOUT
= 1.23 × R1 + R2
R2
R2 can be as high as 100kΩ, but a typical value
is 10kΩ. Using that value, R1 is determined by:
R1 = 8.18 × (VOUT − 1.23)
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 17kΩ.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value inductor
will result in less ripple current that will result in
lower output ripple voltage. However, the larger
value inductor will have a larger physical size,
higher series resistance, and/or lower saturation
current. A good rule for determining the
inductance to use is to allow the peak-to-peak
ripple current in the inductor to be approximately
30% of the maximum switch current limit. Also,
make sure that the peak inductor current is below
the maximum switch current limit. The inductance
value can be calculated by:
L
=
VOUT
fS × ΔIL
× ⎜⎜⎝⎛1−
VOUT
VIN
⎟⎟⎠⎞
Where fS is the switching frequency, ΔIL is the
peak-to-peak inductor ripple current and VIN is the
input voltage.
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