WM8993 datasheet(94/229 Pages) WOLFSON

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WM8993

Production Data

PD, November 2010, Rev 4.0

HEADPHONE OUTPUT CONFIGURATIONS

The headphone outputs HPOUT1L andHPOUT1R are driven by the headphone output PGAs

HPOUT1LVOL and HPOUT1RVOL. Each PGA has its own dedicated volume control, as described

in the “Output Signal Path” section. The input to these PGAs can be either the output mixers

MIXOUTL and MIXOUTR or the direct DAC outputs DACL and DACR.

The headphone output driver is capable of driving up to 25mW into a 16Ω or 32Ω 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

outputs, suppressing ‘pop’ noise and minimising power consumption. The Charge Pump and DC

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

It is recommended to connect a zobel network to the headphone output pins HPOUT1L and

HPOUT1R for best audio performance in all applications. The components of the zobel network 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. 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 27.

If any ground-referenced headphone output is not used, then the zobel network components can be

omitted from the corresponding output pin, and the pin can be left floating. The respective

headphone driver(s) should not be enabled in this case.

Figure 27 Zobel Network Components for HPOUT1L and HPOUT1R

The headphone output incorporates a common mode, or ground loop, feedback path which provides

rejection of system-related ground noise. The return path is via HPOUT1FB. This pin must be

connected to ground for normal operation of the headphone output. No register configuration is

required.

Note that the HPOUT1FB pin should be connected to GND close to the headphone jack, as

illustrated in Figure 27.

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