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AS1329

Low Voltage, Micropower, DC-DC Step-Up Converters

austriamicrosystems AG 

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:

IOUT(MAX) = η ⋅ ⎝⎛IP – V-f---⋅-I--NL----⋅-⋅--D-2--⎠⎞ ⋅ (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

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)

Manufacturer

1A

1.5A

6.8x6.0x2.4mm

6.8x6.0x2.4mm

Coilcraft

www.coilcraft.com

1.8A

6.8x6.0x2.4mm

0.61A

0.76A

6.9x5.0x2.0mm

6.9x5.0x2.0mm

Sumida

www.sumida.com

0.95A

4.8x4.3x3.5mm

0.84A

6.9x5.0x2.0mm

www.austriamicrosystems.com

Revision 1.01

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