WM8994 Datasheet, PDF (347/359 Pages) Wolfson Microelectronics plc – Multi-Channel Audio Hub CODEC for Smartphones

Production Data
WM8994
EARPIECE DRIVER OUTPUT PATH
The earpiece driver on HPOUT2P and HPOUT2N is designed as a 32ohm BTL speaker driver. The
outputs are referenced to the internal DC reference VMID, but direct connection to the speaker is
possible because of the BTL configuration. There is no requirement for DC blocking capacitors.
LINE OUTPUT PATHS
The WM8994 provides four line outputs (LINEOUT1P, LINEOUT1N, LINEOUT2P and LINEOUT2N).
Each of these outputs is referenced to the internal DC reference, VMID. In any case where a line
output is used in a single-ended configuration (i.e. referenced to AGND), a DC blocking capacitor will
be required in order to remove the DC bias. In the case where a pair of line outputs is configured as a
BTL differential pair, then the DC blocking capacitor should be omitted.
The choice of capacitor is determined from the filter that is formed between the capacitor and the load
impedance – see Figure 88.
Figure 88 Line Output Path Components
LOAD IMPEDANCE
MINIMUM CAPACITANCE
FOR 20HZ PASS BAND
10k
0.8 F
47k
0.17 F
Table 147 Line Output Frequency Cut-Off
Using the figures in Table 147, it follows that that a 1F capacitance would be a suitable choice for a
line load. Tantalum electrolytic capacitors are again particularly suitable but ceramic equivalents are a
cost effective alternative. Care must be taken to ensure the desired capacitance is maintained at the
appropriate operating voltage.
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PD, April 2012, Rev 4.4
347