APW7136BCI-TRG 데이터 시트보기 (PDF) - Anpec Electronics
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APW7136BCI-TRG Datasheet PDF : 17 Pages
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APW7136A/B/C
Application Information
Input Capacitor Selection
The input capacitor (C ) reduces the ripple of the input
IN
current drawn from the input supply and reduces noise
injection into the IC. The reflected ripple voltage will be
smaller when an input capacitor with larger capacitance
is used. For reliable operation, it is recommended to
select the capacitor with maximum voltage rating at least
1.2 times of the maximum input voltage. The capacitors
should be placed close to the VIN and the GND.
Inductor Selection
Selecting an inductor with low DC resistance reduces
conduction losses and achieves high efficiency. The effi-
ciency is moderated whilst using small chip inductor
which operates with higher inductor core losses.
Therefore, it is necessary to take further consideration
while choosing an adequate inductor. Mainly, the induc-
tor value determines the inductor ripple current: larger
inductor value results in smaller inductor ripple current
and lower conduction losses of the converter. However,
larger inductor value generates slower load transient
response. A reasonable design rule is to set the ripple
current, ∆IL, to be 30% to 50% of the maximum average
inductor current, IL(AVG). The inductor value can be ob-
tained as below,
L
≥
VIN
VOUT
2
×
VOUT − VIN
FSW ⋅ IOUT(MAX)
×
η
∆IL
IL(AVG)
where
VIN = input voltage
V = output voltage
OUT
F = switching frequency in MHz
SW
IOUT = maximum output current in amp.
η = Efficiency
∆IL /IL(AVG) = inductor ripple current/average current
(0.3 to 0.5, typical)
To avoid the saturation of the inductor, the inductor should
be rated at least for the maximum input current of the
converter plus the inductor ripple current. The maximum
input current is calculated as below:
IIN(MAX )
=
IOUT(MAX) ⋅ VOUT
VIN ⋅ η
The peak inductor current is calculated as the following
equation:
( ) IPEAK
= IIN(MAX)
+
1 ⋅ VIN ⋅ VOUT − VIN
2 VOUT ⋅ L ⋅ FSW
VIN IIN
IL
LX
D1
IOUT VOUT
CIN
N-FET ISW
ESR
COUT
IL
ILIM
IPEAK
∆IL
IIN
ISW
ID
IOUT
Output Capacitor Selection
The current-mode control scheme of the APW7136 al-
lows the usage of tiny ceramic capacitors. The higher
capacitor value provides good load transients response.
Ceramic capacitors with low ESR values have the lowest
output voltage ripple and are recommended. If required,
tantalum capacitors may be used as well. The output ripple
is the sum of the voltages across the ESR and the ideal
output capacitor.
ΔV = ΔV + ΔV
OUT
ESR
COUT
∆VCOUT
≈
IOUT
COUT
⋅
VOUT
VOUT
− VIN
⋅ FSW
∆VESR ≈ IPEAK ⋅ RESR
where IPEAK is the peak inductor current.
Copyright © ANPEC Electronics Corp.
11
Rev. A.4 - Dec., 2010
www.anpec.com.tw
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