WM8311 datasheet(289/302 Pages) WOLFSON

289 / 302 page

Pre-Production

WM8311

PP, May 2012, Rev 3.1

289

For detailed schematics, bill of materials and recommended external components refer to the

WM8311 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 41.

Figure 41 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:

WM8311 Datasheet(PDF) 289 Page - Wolfson Microelectronics plc