WM8750JL
Production Data
THERMAL SHUTDOWN
The speaker and headphone outputs can drive very large currents. To protect the WM8750JL from
overheating a thermal shutdown circuit is included. If the device temperature reaches approximately
150°C and the thermal shutdown circuit is enabled (TSDEN = 1 ) then the speaker and headphone
amplifiers (outputs OUT1L/R, OUT2L/R and OUT3) will be disabled.
REGISTER
ADDRESS
BIT
LABEL
TSDEN
DEFAULT
DESCRIPTION
R23 (17h)
8
0
Thermal Shutdown Enable
0 : thermal shutdown disabled
1 : thermal shutdown enabled
Additional
Control (1)
Table 33 Thermal Shutdown
HEADPHONE OUTPUT
Analogue outputs LOUT1/ROUT1, LOUT2/ROUT2, and OUT3, can drive a 16 or 32 headphone
load, either through DC blocking capacitors, or DC coupled without any capacitor.
DC Coupled Headphone Output
(OUT3SW = 00)
Headphone Output using DC blocking
capacitors
Figure 13 Recommended Headphone Output Configurations
When DC blocking capacitors are used, then their capacitance and the load resistance together
determine the lower cut-off frequency, fc. Increasing the capacitance lowers fc, improving the bass
response. Smaller capacitance values will diminish the bass response. Assuming a 16 Ohm load and
C1, C2 = 220F:
fc = 1 / 2 RLC1 = 1 / (2 x 16 x 220F) = 45 Hz
In the DC coupled configuration, the headphone “ground” is connected to the OUT3 pin, which must
be enabled by setting OUT3 = 1 and OUT3SW = 00. As the OUT3 pin produces a DC voltage of
AVDD/2 (=VREF), there is no DC offset between LOUT1/ROUT1 and OUT3, and therefore no DC
blocking capacitors are required. This saves space and material cost in portable applications.
It is recommended to connect the DC coupled headphone outputs only to headphones, and not to the
line input of another device. Although the built-in thermal shutdown circuit will prevent any damage to
the headphone outputs if overloaded, such a connection may be noisy, and may not function properly
if the other device is grounded.
SPEAKER OUTPUT
LOUT2 and ROUT2 can differentially drive a mono 8 speaker as shown below.
LEFT
MIXER
LOUT2
LOUT2VOL
VSPKR = L-(-R) = L+R
ROUT2INV = 1
-1
ROUT2
RIGHT
MIXER
ROUT2VOL
Figure 14 Speaker Output Connection
PD, April 2012, Rev 4.1
36
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
