WM8993 datasheet(220/229 Pages) WOLFSON

220 / 229 page

WM8993

Production Data

PD, November 2010, Rev 4.0

220

HEADPHONE OUTPUT PATH

The headphone output on WM8993 is ground referenced and therefore does not require the large,

expensive capacitors necessary for VMID reference solutions. For best audio performance, it is

recommended to connect a zobel network to the audio output pins. This network should comprise of

a 100nF capacitor and 20ohm resistor in series with each other (see “Analogue Outputs” section).

These components have the effect of dampening high frequency oscillations or instabilities that can

arise outside the audio band under certain conditions. Possible sources of these instabilities include

the inductive load of a headphone coil or an active load in the form of an external line amplifier.

EARPIECE DRIVER OUTPUT PATH

The earpiece driver on HPOUT2P and HPOUTN 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 WM8993 provides four line outputs (LINEOUT1P, LINEOUT1N, LINEOUT2P and LINEOUT2N).

Each of these outputs is referenced to the internal DC reference, VMID. In any the 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 86.

Figure 86 Line Output Path Components

LOAD IMPEDANCE

MINIMUM CAPACITANCE

FOR 20HZ PASS BAND

10k

0.8

μF

47k

0.17

μF

Table 116 Line Output Frequency Cut-Off

Using the figures in Table 116, it follows that that a 1

μF 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.

WM8993 Datasheet(PDF) 220 Page - Wolfson Microelectronics plc