WM8753LEBSLASHV datasheet(47/87 Pages) WOLFSON

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WM8753L

Advanced Information

AI Rev 3.1 June 2004

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R27 (1Bh)

GPIO Control

(1)

4:3

GPIO4M[2:0]

Configures GPIO4 pin:

000 = Input only.

001 = unused.

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

150

0C 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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R45 (2Dh)

Output

Control

TSDEN

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 16

Ω or 32Ω

headphone load, either through DC blocking capacitors, or DC coupled without any capacitor.

Headphone Output using DC blocking capacitors

DC Coupled Headphone Output

(OUT3SW = 00 or OUT4SW=00)

WM8753L

C2 220uF

LOUT1/2

ROUT1/2

HPGND = 0V

C1 220uF

WM8753L

LOUT1/2

ROUT1/2

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 16

Ω load and C1,

C2 = 220

µF:

fc = 1 / 2

π R

LC1 = 1 / (2

π 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.

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