WM8310 Datasheet, PDF (282/291 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

WM8310
Pre-Production
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.
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
L
C_OUT
C_IN
FET +
shottky diode
VALUE
10H
4.7F
3.3F
1.5F
2.2F
PART NUMBER
Taiyo-Yuden NR3015T100M
Murata GRM31CR61C475KA01
Murata GRM31CR71C335KA01
MuRata GRM31CR71H225KA88
MuRata GRM188R61A5KE34
Vishay SIA814DJ-T1-GE3
R1
1.8M
Phycomp 2322 7046 1805
R2
47k
Multicomp MIC 0.063W 0603 1% 47K
Table 110 Recommended External Components - DC-DC4
SIZE
3 x 3 x 1.5mm
1206
1206
1206
0603
SC-70-6
2.05 x 2.05 x
0.75mm
0603
0603
w
PP, May 2012, Rev 3.1
282