WM8753L
Advanced Information
REGISTER
ADDRESS
BIT
4:3
LABEL
DEFAULT
00
DESCRIPTION
Configures GPIO4 pin:
000 = Input only.
001 = unused.
R27 (1Bh)
GPIO Control
(1)
GPIO4M[2:0]
010 = input only with pull-down.
011 = Input only with pull-up.
100 = Drive low.
101 = Drive high.
110 = SDOUT from control interface
111 = INT from interrupt controller
Table 46 GPIO4 Control
THERMAL SHUTDOWN
The speaker and headphone outputs can drive very large currents. To protect the WM8753L from
overheating a thermal shutdown circuit is included. If the device temperature reaches approximately
1500C and the thermal shutdown circuit is enabled (TSDEN = 1 ) then the speaker and headphone
amplifiers (outputs OUT1L/R, OUT2L/R, OUT3 and OUT4) will be disabled if TSDADEN is set. The
thermal shutdown may also be configured to generate an interrupt. See the GPIO and Interrupt
Controller section for details.
REGISTER
ADDRESS
BIT
LABEL
TSDEN
DEFAULT
DESCRIPTION
R45 (2Dh)
Output
Control
4
6
0
0
Thermal Shutdown Enable
1 : thermal shutdown disabled
0 : thermal shutdown enabled
R63 (3Fh)
Additional
Control
TSDADEN
Thermal Shutdown Control
0 : Thermal shutdown will not disable
speaker and headphone outputs
1 : Thermal shutdown will automatically
disable speaker and headphone outputs
Table 47 Thermal Shutdown
HEADPHONE OUTPUT
Analogue outputs LOUT1/ROUT1, LOUT2/ROUT2, and OUT3/OUT4, can drive a 16Ω or 32Ω
headphone load, either through DC blocking capacitors, or DC coupled without any capacitor.
DC Coupled Headphone Output
Headphone Output using DC blocking capacitors
(OUT3SW = 00 or OUT4SW=00)
C1 220uF
LOUT1/2
LOUT1/2
ROUT1/2
WM8753L
WM8753L
C2 220uF
ROUT1/2
HPGND = 0V
OUT3/OUT4 = VREF
Figure 11 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 16Ω load and C1,
C2 = 220µF:
fc = 1 / 2π RLC1 = 1 / (2π x 16Ω x 220µF) = 45 Hz
In the DC coupled configuration, the headphone “ground” is connected to the OUT3 or OUT4 pin.
OUT3 is enabled by setting OUT3 = 1 and OUT3SW = 00, while OUT4 is enabled by setting OUT4=1
and OUT4SW=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.
AI Rev 3.1 June 2004
w
47
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
