AS1322
Data Sheet
- Application Information
External Component Selection
Inductor Selection
The fast switching frequency (1.2MHz) of the AS1322 allows for the use of small surface mount or chip inductor for the
external inductor
The required minimum values for the external inductor are:
!
!
3.3µH for applications
≤
3.6V
4.7µH for applications > 3.6V
Larger inductor values allow greater output current capability by reducing the inductor ripple current. Increasing the
inductance above 10µH will increase size while providing negligible improvement in output current capability.
The approximate output current capability of the AS1322 versus inductor value is given in:
V
IN
⋅
D
-
I
OUT
(
MAX
)
=
η ⋅ ⎛
I
P
–
-----------------
⎞ ⋅ (
1
–
D
)
⎝
f
⋅
L
⋅
2
⎠
Where:
η
is the estimated efficiency;
I
P
is the peak current limit value (0.6A);
V
IN
is the input voltage;
D is the steady-state duty ratio = (V
OUT
- V
IN
)/V
OUT
;
f is the switching frequency (1.2MHz typ);
L is the inductor value.
The inductor current ripple is typically set for 20 to 40% of the maximum inductor current (I
P
). High-frequency ferrite
core inductor materials reduce frequency dependent power losses compared to less expensive powdered iron types,
which result in improved converter efficiency.
The inductor should have low ESR to reduce the I R power losses, and must be able to handle the peak inductor cur-
rent without saturating. Molded chokes and some chip inductors normally do not have enough core to support the peak
inductor currents of the AS1322 (850mA typ). To minimize radiated noise, use a toroid, pot core, or shielded bobbin
inductor.
Table 5. Recommended Inductors
Part Number
MOS6020-103ML
MOS6020-472ML
MOS6020-332ML
CDRH4D18-100
CDRH4D18-6R8
CR43-6R8
CDRH4D18-4R7
L
10µH
4.7µH
3.3µH
10µH
6.8µH
6.8µH
4.7µH
DCR
93mΩ
50mΩ
46mΩ
200mΩ
200mΩ
131.2mΩ
162mΩ
Current Rating Dimensions (L/W/T)
1A
1.5A
1.8A
0.61A
0.76A
0.95A
0.84A
6.8x6.0x2.4mm
6.8x6.0x2.4mm
6.8x6.0x2.4mm
6.9x5.0x2.0mm
6.9x5.0x2.0mm
4.8x4.3x3.5mm
6.9x5.0x2.0mm
Sumida
Manufacturer
Coilcraft
2
(EQ 2)
www.austriamicrosystems.com
Revision 1.07
11 - 17
AMSCO [ AUSTRIAMICROSYSTEMS AG ]
