APW7101 データシートの表示（PDF） - Anpec Electronics
部品番号
コンポーネント説明
メーカー
APW7101 Datasheet PDF : 16 Pages
| |||
APW7101
Application Information
Inductor Selection
Due to the high switching frequency as 1.5MHz, the in-
ductor value of the application field of APW7101 is usually
from 1µH to 4.7µH. The criterion to select a suitable in-
ductor is dependent on the worst current ripple through-
out the inductor. The worst current ripple defines as 40%
of the fully load capability. In the APW7101 applications,
the worst value of current ripple is 240mA, the 40% of
600mA. Evaluate L by equation (1):
( ) L = VIN − VOUT ⋅ VOUT ⋅ 1
......( 1)
VIN
∆IL ⋅ fS
Figure-1 shows a schematic of a Buck structure. The
waveforms is shown as Figure-2.
IL
IOUT
IIN
0A
0A
IIN
I(CIN)
where
f
S
is
the
switching
frequency
of
APW7101
and
∆IL
is
the value of the worst current ripple, it can be any value of
current ripple that smaller than the worst value you can
accept. In order to perform high efficiency, selecting a low
DC resistance inductor is a helpful way. Another impor-
tant parameter is the DC current rating of the inductor.
The minimum value of DC current rating equals the full
load value of 600mA, plus the half of the worst current
ripple, 120mA. Choose inductors with suitable DC
current rating to ensure the inductors don’t operate in the
saturation.
Input Capacitor Selection
The input capacitor must be able to support the maxi-
mum input operating voltage and maximum RMS input
current. The Buck converter absorbs current from input in
pulses.
0A
I(COUT)
I(Q1)
IOUT
0A
D*TS
(1-D)*TS
PWM
0A
Figure-2
Observe the waveform of I(C ),the RMS value of I(C ) is
IN
IN
[ ] ( ) ( ) ( ) I CIN =
IOUT − IIN 2 ⋅
2
D + IIN ⋅
2
1− D
......(2)
Replace D and IIN by following relation:
D = VOUT ......(3)
VIN
IIN = D ⋅IOUT ......(4)
The RMS value of input capacitor current equal:
( ) I CIN = IOUT ⋅ D(1− D) ......(5)
Figure-1
When D=0.5 the RMS current of input capacitor will be
maximum value. Use this value to choose the input
capacitor with suitable current rating.
Copyright © ANPEC Electronics Corp.
10
Rev. A.4 - Jun., 2008
www.anpec.com.tw
Share Link: 