WM8321
Production Data
As a minimum requirement, the DC current rating should be equal to the maximum load current plus
one half of the inductor current ripple:
To be suitable for the application, the chosen inductor must have a saturation current that is higher
than the peak inductor current given by the above equation. To maximise the converter efficiency, the
inductor should also have a low DC Resistance (DCR), resulting in minimum conduction losses. Care
should also be taken to ensure that the component’s inductance is valid at the applicable operating
temperature.
The WM8321 incorporates a current-limit protection feature for all DC-DC Converter outputs. In order
to achieve the benefit of this feature, the output inductor saturation current limit must be greater than
or equal to the P-channel Current Limit for the applicable converter (see Section 7).
Wolfson recommends the following external components for use with DC-DC Converters 1 and 2.
The output inductor must be consistent with the DCm_FREQ register settings. The supported
configurations are listed in Table 84. Note that for output voltages greater than 1.4V, the 2MHz mode
must be used.
DCm_FREQ
SWITCHING
FREQUENCY
OUTPUT
INDUCTOR
COMMENTS
00
01
10
11
n/a
n/a
n/a
2MHz
4MHz
4MHz
2.2H
1.0H
0.5H
Best efficiency
Good transient performance and efficiency
Best transient performance
Table 84 Output Inductor Selection - DC-DC1, DC-DC2
The output capacitor must be consistent with the DCm_CAP register settings. For best performance,
the 47F component is recommended. For typical applications, the 22F is suitable. The alternative
values may be used for size or cost reasons if preferred.
COMPONENT
VALUE
0.5H
1.0H
2.2H
47F
PART NUMBER
SIZE
1.9 x 2 x 1mm
3 x 3 x 1.2mm
3 x 3 x 1.5mm
0805
L
Coilcraft XPL2010-501ML_
Coilcraft XFL3012-102ME_
Coilcraft LPS3015-222ML_
COUT
MuRata GRM21BR60G476MEA1
MuRata GRM21BR60J226ME39
MuRata GRM188R60J106ME84
MuRata GRM188R60J475ME84
MuRata GRM188R60J106ME84
22F
0805
10F
0603
4.7F
10F
0603
CIN
0603
Table 85 Recommended External Components - DC-DC1, DC-DC2
PD, February 2012, Rev 4.0
246
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
