
AS1329
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.3 External Component Selection
The fast switching frequency (1.2MHz) of the AS1329 allows for the use of small surface mount or chip inductor for the external inductor (see
Figure 19 on page 8) .
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 AS1329 versus inductor value is given in:
I OUT ( MAX ) = η ? ? I P – ------------------ ? ? ( 1 – D )
f ? L ? 2 ?
?
V IN ? D
(EQ 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 I2R power losses, and must be able to handle the peak inductor current without saturating.
Molded chokes and some chip inductors normally do not have enough core to support the peak inductor currents of the AS1329 (850mA typ). To
minimize radiated noise, use a toroid, pot core, or shielded bobbin inductor.
Table 6. 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
93m ?
50m ?
46m ?
200m ?
200m ?
131.2m ?
162m ?
Current Rating
1A
1.5A
1.8A
0.61A
0.76A
0.95A
0.84A
Dimensions (L/W/T)
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
Coilcraft
www.coilcraft.com
Sumida
www.sumida.com
www.ams.com/DC-DC_Step-Up/AS1329
Revision 1.12
14 - 20