wm8903 Wolfson Microelectronics plc, wm8903 Datasheet - Page 153

• Manufacturer Part Number: wm8903
• Description: Ultra Low Power Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Pre-Production
APPLICATIONS INFORMATION
RECOMMENDED EXTERNAL COMPONENTS
Figure 64 Recommended External Components
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Design notes
(1) Capacitor Type
Decouplers: For C3, C4, C8, C9, a single 4.7uF X5R ceramic can be used.
Charge pump capacitor types are critical. Capacitors must meet DC co-efficient requirement. See datasheet text.
AC coupling capacitors: C6, C7, C10, C11, C12 and C13 are recommended to be Tantalum with low ESR.
(2) Capacitor positioning
Decouplers and charge pump capacitors should be positioned as close to WM8903 as possible.
C8, C9, C16 are the most important. C1, C2, C3, C4, C17, C18 should also be very close to WM8903.
(3) Zobel Network
All Zobel networks are a requirement if either HPOUT or LINEOUT is used. See datasheet text.
Zobel Network should be positioned reasonably close to WM8903
(4) R3 and R4
R3 and R4 can be populated with other values to remove common mode noise on the microphone
As well as selection of correct capacitor values, together with careful PCB layout, it is important to
select the correct capacitor type for the charge pump. Capacitors generally reduce in value as the
DC bias voltage across the capacitor is increased, this is known as the voltage coefficient of the
capacitor. Verifying that the required capacitance can be met at the specified DC voltage depends on
the capacitor design, so the individual capacitor datasheet must be consulted. The requirements of
each capacitor, and some example capacitor parts are detailed in Table 77, and also discussed in
the application note “WAN0214: External Component Requirements for Ground Referenced
Outputs”. Audio performance may be impacted if the capacitor does not meet the capacitance
requirements at a given DC voltage.
PP, Rev 3.1, August 2009
WM8903
153