wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 203

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

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Pre-Production
DC-DC CONVERTER COMPONENT SELECTION
The DC-DC Converters use an integral loop compensation circuit, requiring external components to
be connected. The recommended external component connections are illustrated in Figure 106.
Figure 106 DC-DC 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 for DC-DC1 and DC-DC2 varies depending on the required transient
response. A value of 22µF is recommended in the first instance. Larger values (up to 47µF) 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 fields DC1_CAP and DC2_CAP must be set according to the
output capacitance, as detailed in Table 107.
Table 107 Register Control for DC-DC1 and DC-DC2 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.
DC Converter enabled by logic
high input to DC1EN (referenced
to HBVDD power domain).
Start-up voltage determined by
logic level or analogue feedback
connection to DC1VSEL
R71 (47h)
DCDC1
Control 2
R73 (49h)
DCDC2
Control 2
ADDRESS
DC1EN
DC1VSEL
15:14
15:14
BIT
DC1_CAP
DC2_CAP
LABEL
2.7V – 5.5V
DC1VDD
WM8400
DC1
DEFAULT
01
01
Note: Equivalent circuit applies for DC2.
C
IN
DC-DC1 Output Capacitor
00 = Reserved
01 = 10µF
10 = 22µF
11 = 47µF
DC-DC2 Output Capacitor
00 = Reserved
01 = 10µF
10 = 22µF
11 = 47µF
DC1FB
DC1LX
DC1GND
Recommended component values:
L = 2.2uH
C
C
DESCRIPTION
C
OUT
IN
L
OUT
= 4.7uF
= 22uF
PP, April 2009, Rev 3.0
V
O
Load
WM8400
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