WM8987 Datasheet, PDF (54/59 Pages) Wolfson Microelectronics plc – Stereo CODEC for Portable Audio Applications

WM8987L
Production Data
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.
w
PD Rev 4.0 August 2008
54