AS1323 データシートの表示（PDF） - austriamicrosystems AG

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AS1323

1.6µA Quiescent Current, Single Cell, DC-DC Step-Up Converter

austriamicrosystems AG 

AS1323

Data Sheet - Application Information

9 Application Information

Figure 12. Typical Application

10µH

1

5

VBATT

LX

10µF

AS1323 2

VSS

3

SHDNN

4

VOUT

10µF

Inductor Selection

The control scheme of the AS1323 allows for a wide range if inductor values. A 10µH inductor should be sufficient for

most applications (see Figure 12).

Smaller inductance values typically offer smaller physical size for a given series resistance, allowing the smallest over-

all circuit dimensions. Applications using larger inductance values may startup at lower battery voltages, provide higher

efficiency and exhibit less ripple, but they may reduce the maximum output current. This occurs when the inductance is

sufficiently large to prevent the maximum current limit (ILIMIT) from being reached before the maximum on-time (tON)

expires (see Electrical Characteristics on page 4).

For maximum output current, the inductor value should be chosen such that the controller reaches the current-limit

before the maximum on-time is triggered:

L > -V----B----A---T----T----⋅---t--O----N--

ILIMIT

(EQ 1)

tONMAX is 6µs (typ).

ILIMIT is 400mA (typ).

For larger inductor values, the peak inductor current (IPEAK) can be determined by:

The inductor’s incremental saturation current rating should be greater than the peak switching current. However, it is

IPEAK

=

V-----B----A---T----T----⋅---t--O----N--

L

(EQ 2)

generally advisable to bias the inductor into saturation by as much as 20%, although this will slightly reduce efficiency.

Maximum Output Current

The maximum output current (IOUTMAX) is a function of IPEAK, VIN, VOUT, and the overall efficiency (η) as indicated in

the formula for determining IOUTMAX:

IOUTMAX

=

1--

2

⋅

IPEAK

⋅

⎛

⎝

V--V---B-O--A--U--T--T-T-⎠⎞

⋅η

(EQ 3)

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