WM8321 Datasheet, PDF (246/253 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

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
00
01
10
11
SWITCHING
FREQUENCY
n/a
2MHz
4MHz
4MHz
OUTPUT
INDUCTOR
n/a
2.2H
1.0H
0.5H
COMMENTS
n/a
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 47F component is recommended. For typical applications, the 22F is suitable. The alternative
values may be used for size or cost reasons if preferred.
COMPONENT
VALUE
PART NUMBER
L
0.5H
Coilcraft XPL2010-501ML_
1.0H
Coilcraft XFL3012-102ME_
2.2H
Coilcraft LPS3015-222ML_
COUT
47F
22F
MuRata GRM21BR60G476MEA1
MuRata GRM21BR60J226ME39
10F
MuRata GRM188R60J106ME84
4.7F
MuRata GRM188R60J475ME84
CIN
10F
MuRata GRM188R60J106ME84
Table 85 Recommended External Components - DC-DC1, DC-DC2
SIZE
1.9 x 2 x 1mm
3 x 3 x 1.2mm
3 x 3 x 1.5mm
0805
0805
0603
0603
0603
w
PD, February 2012, Rev 4.0
246