AS1329
Data Sheet - Application Information
External Component Selection
Inductor 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 15 on page 7).
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:
VIN ⋅ D
f ⋅ L ⋅ 2
⎛
⎞
⎠
-----------------
IOUT(MAX) = η ⋅ IP –
⋅ (1 – D)
(EQ 2)
⎝
Where:
η is the estimated efficiency;
IP is the peak current limit value (0.6A);
VIN is the input voltage;
D is the steady-state duty ratio = (VOUT - VIN)/VOUT;
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 (IP). 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 cur-
rent 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 5. Recommended Inductors
Part Number
MOS6020-103ML
MOS6020-472ML
MOS6020-332ML
CDRH4D18-100
CDRH4D18-6R8
CR43-6R8
L
DCR
93mΩ
Current Rating Dimensions (L/W/T)
Manufacturer
Coilcraft
www.coilcraft.com
10µH
4.7µH
3.3µH
10µH
6.8µH
6.8µH
4.7µH
1A
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
50mΩ
1.5A
46mΩ
1.8A
Sumida
www.sumida.com
200mΩ
200mΩ
131.2mΩ
162mΩ
0.61A
0.76A
0.95A
0.84A
CDRH4D18-4R7
www.austriamicrosystems.com
Revision 1.01
11 - 17
AMSCO [ AMS(艾迈斯) ]
