AS1326
Datasheet - Application Information
Inductor Selection
The AS1326A/AS1326B high switching-frequency allows the use of a small 3.3µH surface-mount inductor. The induc-
tor should generally have a saturation current rating exceeding the N-channel switch current limit; however, it is
acceptable to bias the inductor current into saturation by as much as 20% if a slight reduction in efficiency is accept-
able.
Lower current-rated inductors may be used if ISET is used to reduce the peak inductor current (see Setting the Switch
Current Limit on page 12). For high efficiency, select an inductor with a high-frequency ferrite core material to reduce
core losses. To minimize radiated noise, use a toroid or shielded inductor. Connect the inductor from the battery to the
pin LX as close to the device as possible.
Table 7. Recommended Inductors
Part Number
MOS6020-332
LPS4018-332
DO1608C-272
L
DCR
46mΩ
80mΩ
80mΩ
Current Rating Dimensions (L/W/T)
Manufacturer
Coilcraft
www.coilcraft.com
3.3µH
3.3µH
2.7µH
1.8A
2.0A
2.1A
6.8x6.0x2.4mm
4x4x1.8mm
6.6x4.45x2.92mm
Sumida
www.sumida.com
CDRH5D18NP-4R1N
4.1µH
57mΩ
1.95A
6x6x2mm
Figure 23. Efficiency vs. IOUT; VIN = 2V, VOUT = 3.3V
Figure 24. Efficiency vs. IOUT; VIN = 3V, VOUT = 5V
96
94
92
90
88
86
84
82
80
78
76
96
94
92
90
88
86
84
82
80
MOS6020-332
DO1608C-272
CDRH5D18NP-4R1N
LPS4018-332
MOS6020-332
DO1608C-272
CDRH5D18NP-4R1N
LPS4018-332
74
72
78
70
76
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
External Schottky Diode
For output voltages greater than 4V, an external Schottky diode must be connected between pin LX and POUT, in par-
allel with the integrated synchronous rectifier (see Figure 25). The diode should be rated for 0.5A. An external diode is
also recommended for applications that must start with input voltages at or below 1.8V. The Schottky diode carries cur-
rent during startup and after the synchronous rectifier turns off; thus, its current rating only needs to be 500mA.
Note: Connect the diode as close to the IC as possible.
For circuits that do not require startup with inputs below 1.8V and have an output of 4V or less, the external
diode is not needed.
Caution: Do not use ordinary rectifier diodes as their slow switching speeds and long reverse-recovery times render
them unacceptable.
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