WM9090ECSSLASHR datasheet(32/81 Pages) WOLFSON

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WM9090

Production Data

PD, November 2010, Rev 4.1

HEADPHONE OUTPUT CONFIGURATIONS

The headphone output pins HPOUTL and HPOUTR are driven by the headphone output PGAs. Each

PGA has its own dedicated volume control, as described in the “Output Signal Path” section. The

inputs to these PGAs come from the respective output mixers MIXOUTL or MIXOUTR.

The headphone output driver is capable of driving up to 35mW into a 16Ω load such as a stereo

headset or headphones. The outputs are ground-referenced, eliminating any requirement for AC

coupling capacitors. This is achieved by having separate positive and negative supply rails powered

by an on-chip charge pump. A DC Servo circuit removes any DC offset from the headphone outputs,

suppressing ‘pop’ noise and minimising power consumption. The Charge Pump and DC Servo are

described separately (see “Charge Pump” and “DC Servo” respectively).

The zobel network components should be connected to the headphone output pins HPOUTL and

HPOUTR for best audio performance in all applications. The components of the zobel network have

the effect of dampening high frequency oscillations and 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. The capacitance of lengthy

cables or PCB tracks can also lead to amplifier instability. The zobel network should comprise of a

Ω resistor and 100nF capacitor in series with each other, as illustrated in Figure 5.

Figure 5 Zobel Network Components for HPOUTL and HPOUTR

CLOCKING CONTROL

The internal clocks for the WM9090 are derived from a common internal clock source, CLK_SYS.

This clock is the reference for the Control Write Sequencer, Class D switching amplifier, DC servo

control and other internal functions.

CLK_SYS is derived from an internal oscillator; this is controlled by the OSC_ENA register. The

frequency of CLK_SYS is nominally 6MHz; internal dividers generate the other required clocks from

this reference.

A slow clock, TOCLK, is used to set the timeout period for volume updates when zero-cross detect is

used. This clock is derived from CLK_SYS and is enabled by TOCLK_ENA. The slow clock

frequency is selected using the programmable dividers TOCLK_RATE, TOCLK_RATE_X4 and

TOCLK_RATE_DIV16. See Table 17 for a list of possible TOCLK rates.

The clocking configuration is illustrated in Figure 6. The control registers associated with WM9090

Clocking are defined in Table 16.

WM9090ECS/R Datasheet(PDF) 32 Page - Wolfson Microelectronics plc