WM8310 Datasheet, PDF (278/291 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

WM8310
Pre-Production
For detailed schematics, bill of materials and recommended external components refer to the
WM8310 evaluation board users manual.
30.2 VOLTAGE AND CURRENT REFERENCE COMPONENTS
A decoupling capacitor is required between VREFC and REFGND; a 100nF X5R capacitor is
recommended (available in 0201 package size). If USB100MA_STARTUP=1X (see Section 17.4),
then a 50nF capacitor should be used.
A current reference resistor is required between IREFR and REFGND; a 100k (1%) resistor is
recommended.
30.3 DC-DC BUCK CONVERTER EXTERNAL COMPONENTS
The recommended connections to the DC-DC buck converters are illustrated in Figure 34.
Figure 34 DC-DC Synchronous Buck Converter External Components
When selecting suitable capacitors, is it imperative that the effective capacitance is within the
required limits at the applicable input/output voltage of the converter. It should be noted that some
components’ capacitance changes significantly depending on the DC voltage applied. Ceramic X7R
or X5R types are recommended.
The choice of output capacitor varies depending on the required transient response. Larger values
may be required for optimum performance under large load transient conditions. Smaller values may
be sufficient for a steady load, or in applications without stringent requirements on output voltage
accuracy during load transients.
For layout and size reasons, users may choose to implement large values of output capacitance by
connecting two or more capacitors in parallel. To ensure stable operation, the DCm_CAP register
fields must be set according to the output capacitance, as described in Section 15.6.
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 dependant on the inductor value and can be
determined by the following equation:
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PP, May 2012, Rev 3.1
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