APW7334 データシートの表示（PDF） - Anpec Electronics
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APW7334 Datasheet PDF : 15 Pages
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APW7334
Application Information
Setting Output Voltage
The regulated output voltage is determined by:
VOUT = 0.8 × (1 + R1 ) ⋅ ( V )
R2
To prevent stray pickup, please locate resistors R1 and
R2 close to APW7334.
Inductor Capacitor Selection
Use small ceramic capacitors for high frequency
decoupling and bulk capacitors to supply the surge cur-
rent needed each time the N-channel power MOSFET
(Q1) turns on. Place the small ceramic capacitors physi-
cally close to the VIN and between the VIN and GND.
The important parameters for the bulk input capacitor are
the voltage rating and the RMS current rating. For reliable
operation, select the bulk capacitor with voltage and
current ratings above the maximum input voltage and
largest RMS current required by the circuit. The capacitor
voltage rating should be at least 1.25 times greater than
the maximum input voltage and a voltage rating of 1.5
times is a conservative guideline. The RMS current (IRMS)
of the bulk input capacitor is calculated as the following
equation:
T=1/FOSC
VLX
DT
IL
IQ1
ICOUT
I
IOUT
I
VOUT
IOUT
VOUT
Figure 1. Converter Waveforms
Output Capacitor Selection
An output capacitor is required to filter the output and sup-
ply the load transient current. The filtering requirements
are the function of the switching frequency and the ripple
current (DI). The output ripple is the sum of the voltages,
having phase shift, across the ESR and the ideal output
capacitor. The peak-to-peak voltage of the ESR is calcu-
ated as the following equations:
D = VOUT
VIN
........... (1)
IRMS = IOUT D × (1 − D) ⋅ (A)
where D is the duty cycle of the power MOSFET.
For a through hole design, several electrolytic capacitors
may be needed. For surface mount designs, solid tanta-
lum capacitors can be used, but caution must be exer-
cised with regard to the capacitor surge current rating.
∆ I = V OUT × (1 − D )
F OSC × L
........... (2)
V ESR = ∆ I × ESR
........... (3)
The peak- to-peak voltage of the ideal output capacitor is
calculated as the following equations:
∆VCOUT
=
∆I
8 × FOSC × COUT
........... (4)
IQ1
Q1
Q2
VIN
VIN
CIN
IL
LX L
ICOUT
IOUT
ESR
VOUT
COUT
For the applications using bulk capacitors, the ∆VCOUT is
much smaller than the V and can be ignored. Therefore,
ESR
the AC peak-to-peak output voltage(∆VOUT) is shown below:
∆VOUT = ∆I × ESR ⋅ (V)
........... (5)
For the applications using bulk capacitors, the VESR is
much smaller than the ∆VCOUT and can be ignored.
Therefore, the AC peak-to-peak output voltage(∆VOUT) is to
∆VCOUT.
Copyright © ANPEC Electronics Corp.
8
Rev. A.2 - Dec., 2012
www.anpec.com.tw
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