wm8351 Wolfson Microelectronics plc, wm8351 Datasheet - Page 319

• Manufacturer Part Number: wm8351
• Description: Wolfson Audioplus? Stereo Codec With Power Management
• Manufacturer: Wolfson Microelectronics plc

Production Data
29.2 DC-DC (STEP-DOWN) CONVERTER EXTERNAL COMPONENTS
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The recommended connections to the DC-DC (Step-Down) Converters are illustrated in Figure 88.
Figure 88 DC-DC (Step-Down) Converters 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 for DC-DC1 varies depending on the required transient response. A
value of 30μF is recommended in the first instance. Larger values (up to 100μF) may be required for
optimum performance under large load transient conditions. Smaller values (down to 10μF) may be
sufficient for a steady load in some applications.
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 register field DC1_CAP must be set according to the output
capacitance, as detailed in Table 155.
Table 155 Register Control for DC-DC1 Output Capacitor
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:
R180 (B4h)
ADDRESS
15:14
BIT
DC1_CAP
LABEL
DEFAULT
00
DC-DC1 Output Capacitor
00 = 10uF, 30uF, 45uF
01 = 60uF, 85uF
10 = Not used
11 = 100uF
DESCRIPTION
PD, June 2009, Rev 4.1
WM8351
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