AS1323 查看數據表（PDF） - austriamicrosystems AG
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AS1323 Datasheet PDF : 13 Pages
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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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