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AS1329

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:

Where:

η is the estimated efficiency;

f is the switching frequency (1.2MHz typ);

L is the inductor value.

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

2

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 AS1329 (850mA typ). To minimize radiated noise, use a toroid, pot core, or shielded bobbin

inductor.

Table 5. Recommended Inductors

Part Number

L

DCR

Current Rating Dimensions (L/W/T)

Manufacturer

MOS6020-103ML

10µH

93m

Ω

1A

6.8x6.0x2.4mm

Coilcraft

www.coilcraft.com

MOS6020-472ML

4.7µH

50m

Ω

1.5A

6.8x6.0x2.4mm

MOS6020-332ML

3.3µH

46m

Ω

1.8A

6.8x6.0x2.4mm

CDRH4D18-100

10µH

200m

Ω

0.61A

6.9x5.0x2.0mm

Sumida

www.sumida.com

CDRH4D18-6R8

6.8µH

200m

Ω

0.76A

6.9x5.0x2.0mm

CR43-6R8

6.8µH

131.2m

Ω

0.95A

4.8x4.3x3.5mm

CDRH4D18-4R7

4.7µH

162m

Ω

0.84A

6.9x5.0x2.0mm

(EQ 2)

()

IN

D

⋅

fL2

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1D

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