WM8983 datasheet(68/129 Pages) CIRRUS

68 / 129 page

WM8983

Rev 4.6

HEADPHONE OUTPUTS (LOUT1 AND ROUT1)

The headphone outputs LOUT1 and ROUT1 can drive a 16

 or 32 headphone load, either through

DC blocking capacitors, or DC-coupled to a buffered midrail reference as shown in Figure 33. OUT3,

OUT4, LOUT2 or ROUT2 could be used as this buffered reference if one of these outputs is not being

used, saving decoupling capacitors, at the expense of increased power consumption. For fully

independent left and right channels, two separate midrail references can be used, eliminating

crosstalk caused by headphone ground impedances, at the expense of increased power

consumption.

Headphone Output using DC Blocking Capacitors:

WM8983

C2 220uF

LOUT1

ROUT1

AGND1 (= 0V)

C1 220uF

Lowest power consumption (Two outputs enabled);

Large and expensive capacitors;

Bass response may be reduced for smaller capacitors;

Impedance in common ground may introduce crosstalk.

DC Coupled Headphone Output:

WM8983

LOUT1

ROUT1

LOUT2/ROUT2/OUT3/OUT4

= ‘MUTE’ => VMID

Higher power consumption (Three outputs enabled);

Improved PSRR if AVDD2 connected to AVDD1;

Impedance in common ground may introduce crosstalk;

Improved bass response (DC connection).

DC Coupled with Fully Independent Left / Right Drive:

WM8983

LOUT1

ROUT1

LOUT2/OUT3

= ‘MUTE’ => VMID

ROUT2/OUT4

= ‘MUTE’ => VMID

Highest power consumption (Four outputs enabled);

Improved PSRR if AVDD2 connected to AVDD1;

Independent L/R pseudo-ground eliminates crosstalk;

Improved bass response (DC connection);

Non-standard headphone connection may not be suitable

for some applications.

Figure 33 Recommended Headphone Output Configurations

Each headphone output has an analogue volume control PGA with a gain range of -57dB to +6dB.

When DC blocking capacitors are used, their capacitance and the load resistance together determine

the lower cut-off frequency of the output signal, fc. Increasing the capacitance lowers fc, improving the

bass response. Smaller capacitance values will diminish the bass response. Assuming a 16

 load

and C1, C2 = 220

F:

fc = 1 / 2 RLC1 = 1 / (2 x 16 x 220F) = 45 Hz

In the DC coupled configuration, the headphone “ground” is connected to the VMID pin. The OUT3/4

pins can be configured as a DC output driver by setting the OUT3MUTE and OUT4MUTE register bit.

The DC voltage on VMID in this configuration is equal to the DC offset on the LOUT1 and ROUT1

pins; therefore, no DC blocking capacitors are required. This saves space and material cost in

portable applications.

Note that LOUT2, ROUT2, OUT3 and OUT4 have an optional output boost of 1.5x. When these are

configured in this output boost mode (SPKBOOST/OUT3BOOST/OUT4BOOST=1), then the VMID

value of these outputs will be equal to 1.5xAVDD/2 and will not match the VMID of the headphone

drivers. Do not use the DC coupled output mode in this configuration.

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