WM8311 datasheet(293/302 Pages) WOLFSON

293 / 302 page

Pre-Production

WM8311

PP, May 2012, Rev 3.1

293

When selecting a suitable output inductor, the inductance value and the saturation current must be

compatible with the operating conditions of the converter.

The magnitude of the inductor current ripple is dependent on the inductor value and can be

determined by the following equation:

The inductor current is also a function of the DC-DC Converter maximum input current, which can be

determined by the following equation:

As a minimum requirement, the DC current rating should be equal to the maximum input 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 suitable at the applicable

operating temperature.

When ISINK1 or ISINK2 is used in conjunction with DC-DC Converter 4, the ISINK should always be

switched on before the DC-DC Converter is switched on. Conversely, the DC-DC Converter should

always be switched off before the ISINK is switched off.

Wolfson recommends the following external components for use with DC-DC Converter 4.

The output capacitor COUT must be selected according to the required output voltage. For 10V output,

4.7

F is recommended. For 15V output, 3.3F is recommended. For 20-30V output, 1.5F is

recommended.

The resistors R1 and R2 must be selected according to the required output voltage - refer to the

equations above. The values quoted below are suitable for 20V output.

COMPONENT

VALUE

PART NUMBER

SIZE

H

Taiyo-Yuden NR3015T100M

3 x 3 x 1.5mm

COUT

4.7

F

Murata GRM31CR61C475KA01

1206

3.3

F

Murata GRM31CR71C335KA01

1206

1.5

F

MuRata GRM31CR71H225KA88

1206

CIN

2.2

F

MuRata GRM188R61A5KE34

0603

FET +

schottky diode

Vishay SIA814DJ-T1-GE3

SC-70-6

2.05 x 2.05 x

0.75mm

1.8M



Phycomp 2322 7046 1805

0603

47k



Multicomp MIC 0.063W 0603 1% 47K

0603

Table 117 Recommended External Components - DC-DC4

WM8311 Datasheet(PDF) 293 Page - Wolfson Microelectronics plc

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