WM8281ECSSLASHR datasheet(199/392 Pages) CIRRUS

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WM8281

Rev 4.0

199

HEADPHONE OUTPUTS AND MONO MODE

The headphone drivers can provide a mono differential (BTL) output; this is ideal for driving an

earpiece or hearing aid coil. The mono differential (BTL) configuration is selected using the

OUTn_MONO register bits.

When the OUTn_MONO bit is set, then the respective Right channel output is an inverted copy of the

Left channel output signal; this creates a differential output between the respective OUTnL and

OUTnR signal paths. The Left and Right channel output drivers must both be enabled in Mono mode;

both channels should be enabled simultaneously using the register bits described in Table 61.

The mono (BTL) signal paths are illustrated in Figure 56. Note that, in mono configuration, the

effective gain of the signal path is increased by 6dB.

The OUT1L and OUT1R output signal paths are associated with the analogue outputs HPOUT1L and

HPOUT1R respectively.

The OUT2L and OUT2R output signal paths are associated with the analogue outputs HPOUT2L and

HPOUT2R respectively.

The OUT3L and OUT3R output signal paths are associated with the analogue outputs HPOUT3L and

HPOUT3R respectively.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R1040

(0410h)

Output

Path

Config 1L

OUT1_MONO

Output Path 1 Mono Mode

(Configures HPOUT1L and HPOUT1R as

a mono differential output.)

0 = Disabled

1 = Enabled

The gain of the signal path is increased by

6dB in differential (mono) mode.

R1048

(0418h)

Output

Path

Config 2L

OUT2_MONO

Output Path 2 Mono Mode

(Configures HPOUT2L and HPOUT2R as

a mono differential output.)

0 = Disabled

1 = Enabled

The gain of the signal path is increased by

6dB in differential (mono) mode.

R1056

(0420h)

Output

Path

Config 3L

OUT3_MONO

Output Path 3 Mono Mode

(Configures HPOUT3L and HPOUT3R as

a mono differential output.)

0 = Disabled

1 = Enabled

The gain of the signal path is increased by

6dB in differential (mono) mode.

Table 70 Headphone Driver Mono Mode Control

The headphone driver outputs HPOUT1L, HPOUT1R, HPOUT2L, HPOUT2R, HPOUT3L and

HPOUT3R are suitable for direct connection to external headphones and earpieces. The outputs are

ground-referenced, eliminating any requirement for AC coupling capacitors.

The headphone outputs incorporate a common mode, or ground loop, feedback path which provides

rejection of system-related ground noise. The feedback pins must be connected to ground for normal

operation of the headphone outputs.

Note that the feedback pins should be connected to GND close to the respective headphone jack, as

illustrated in Figure 57. In mono (differential) mode, the feedback pin(s) should be connected to the

ground plane that is physically closest to the earpiece output PCB tracks.

The ground feedback path for HPOUT1L and HPOUT1R is provided via the HPOUT1FB1 or

HPOUT1FB2 pins; the applicable connection must be selected using the ACCDET_SRC register, as

described in Table 71.

The ground feedback path for HPOUT2L and HPOUT2R is provided via the HPOUT2FB pin. No

The ground feedback path for HPOUT3L and HPOUT3R is provided via the HPOUT3FB pin. No

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