WM8750LEFLSLASHR datasheet(35/56 Pages) WOLFSON

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WM8750L

PP Rev 1.77 May 2003

THERMAL SHUTDOWN

The speaker and headphone outputs can drive very large currents. To protect the WM8750L 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) will be disabled.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R23 (17h)

Additional

Control (1)

TSDEN

Thermal Shutdown Enable

0 : thermal shutdown disabled

1 : thermal shutdown enabled

Table 31 Thermal Shutdown

HEADPHONE OUTPUT

Analogue outputs LOUT1/ROUT1, LOUT2/ROUT2, and OUT3, 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)

WM8750L

C2 220uF

LOUT1/2

ROUT1/2

HPGND = 0V

C1 220uF

WM8750L

LOUT1/2

ROUT1/2

OUT3 = VREF

Figure 9 Recommended Headphone Output Configurations

When DC blocking capacitors are used, then their capacitance and the load resistance together

determine the lower cut-off frequency, f

c. 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 = 220

µF:

c = 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 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 short circuit protection will prevent any damage

to the headphone outputs, 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

Ω speaker as shown below.

LOUT2

ROUT2

WM8750L

ROUT2INV = 1

SPKR = L-(-R) = L+R

-1

LEFT

MIXER

RIGHT

MIXER

ROUT2VOL

LOUT2VOL

Figure 10 Speaker Output Connection

The right channel is inverted by setting the ROUT2INV bit, so that the signal across the loudspeaker

is the sum of left and right channels.

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