WM8987LGECOSLASHV datasheet(53/58 Pages) WOLFSON

53 / 58 page

Pre-Production

WM8987L

PP Rev 3.0 January 2007

DRIVING BTL HEADSETS

To drive bridge-tied load (BTL) headsets, the analogue outputs should be used as follows:

•

ROUT1 is the non-inverting right output (HPR+)

•

LOUT2 is the non-inverting left output (HPL+)

•

ROUT2 is the inverting right output (HPR-)

•

OUT3 is the inverting left output (HPL-)

This setup is illustrated in Figure 46.

Figure 46 Driving a BTL headset

It requires the following register settings:

•

Set the ROUT1, LOUT2, ROUT2, MONO and OUT3 bits in R26 to ‘1’ to enable the

outputs and associated mixers.

•

Set LD2LO (R34), RD2RO (R37), LD2MO (R38) and OUT3SW (R24) to ‘1’ to enable the

correct audio paths (in the case of audio playback from an analogue source, select the

input pin using LMIXSEL and RMIXSEL, and set LI2LO/LI2MO/RI2RO instead of

LD2LO/LD2MO/RD2RO).

•

Set ROUT2INV = 1 in R24 to invert the right-channel signal going to ROUT2.

•

The left channel volume is controlled by LOUT2VOL and MONOVOL. To get the same

RMS signal level at both pins, MONOVOL should be set 6dB higher than LOUT2VOL.

•

The right channel volume is controlled by ROUT1VOL and ROUT2VOL. Both should be

set to the same value. To get the same gain as in the left channel, this value should be

the same as LOUT2VOL.

Note that this method for driving headsets can only be used where both ends of each transducer are

electrically separate. It is incompatible with standard 2.5mm or 3.5mm headphone jacks, where a

common ground serves as the return path for both left and right transducers.

DRIVING SINGLE-ENDED HEADPHONES

USING CAPACITORS

To drive single-ended headphones using DC blocking capacitors, the analogue outputs should be

used as follows:

•

LOUT2 is the left output

•

ROUT2 is the right output

•

ROUT1 and OUT3 are unused and should be disabled

This setup is illustrated in Figure 47.

WM8987LGECO/V Datasheet(PDF) 53 Page - Wolfson Microelectronics plc

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