Production Data
WM8326
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 WM8326 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 setting. 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
2MHz
4MHz
n/a
n/a
2.2H
1.0H
n/a
n/a
Best efficiency
Best transient performance
n/a
Table 84 Output Inductor Selection - DC-DC1, DC-DC2
The output capacitor must be consistent with the DCm_CAP register setting. For best performance,
the 47F component is recommended. For typical applications, the 22F is suitable; this is the
minimum recommended output capacitor value.
COMPONENT
VALUE
1H
PART NUMBER
SIZE
4 x 4 x 2.1mm
5 x 5 x 4.5mm
4 x 4 x 3.1mm
0805
L
Coilcraft XFL4020-102ME_
TDK VLC5045-2R2N
2.2H
2.2H
47F
22F
22F
Coilcraft XAL4030-222ME_
MuRata GRM21BR60G476MEA1
MuRata GRM21BR60J226ME39
MuRata GRM21BR60J226ME39
COUT
0805
CIN
0805
Table 85 Recommended External Components - DC-DC1, DC-DC2
Wolfson recommends the following external components for use with DC-DC Converters 3 and 4.
Note that the switching frequency of DC-DC3 and DC-DC4 is fixed at 2MHz and the output inductor
must be 2.2H in all cases.
The output capacitor must be consistent with the DCm_CAP register setting. 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.
PD, June 2012, Rev 4.0
249
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
