WM8326 datasheet(249/255 Pages) WOLFSON

249 / 255 page

Production Data

WM8326

PD, June 2012, Rev 4.0

249

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

n/a

2MHz

2.2

H

Best efficiency

4MHz

1.0

H

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 47

F component is recommended. For typical applications, the 22F is suitable; this is the

minimum recommended output capacitor value.

COMPONENT

VALUE

PART NUMBER

SIZE

H

Coilcraft XFL4020-102ME_

4 x 4 x 2.1mm

2.2

H

TDK VLC5045-2R2N

5 x 5 x 4.5mm

2.2

H

Coilcraft XAL4030-222ME_

4 x 4 x 3.1mm

COUT

F

MuRata GRM21BR60G476MEA1

0805

F

MuRata GRM21BR60J226ME39

0805

CIN

F

MuRata GRM21BR60J226ME39

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 2.2

H in all cases.

The output capacitor must be consistent with the DCm_CAP register setting. 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.

WM8326 Datasheet(PDF) 249 Page - Wolfson Microelectronics plc

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