WM8959 datasheet(71/155 Pages) WOLFSON

71 / 155 page

Pre-Production

WM8959

PP, May 2008, Rev 3.1

DISABLED OUTPUTS

Whenever an analogue output is disabled, it can be connected to VREF through a resistor; this

feature is enabled by setting the BUFIOEN bit – see “Pop Suppression Control”. This helps to

prevent pop noise when the output is re-enabled. The resistance between VREF and each output

can be controlled using register bit VROI. By default, a high resistance is used - 20k

Ω for Headphone

outputs (LOUT, ROUT, OUT3 and OUT4) and 10k

Ω for Line outputs (LON, LOP, RON and ROP). If

a low impedance is desired for disabled outputs, VROI can then be set to 1, decreasing the

resistance to about 500

Ω in all cases.

Note that a disabled output may be used as a common ground connection for a capless headphone

output as described earlier.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R55 (37h)

Additional

Control

VROI

VREF to Analogue Output Resistance

(Disabled Outputs)

0 = 20k

Ω (Headphone) or 10kΩ (Line

Out) from buffered VMID to output

1 = 500

Ω from buffered VMID to output

Table 34 Disabled Outputs to VREF Resistance

THERMAL SHUTDOWN

The speaker and headphone outputs can drive very large currents. To protect the WM8959 from

overheating a thermal shutdown circuit is included. If the device temperature reaches approximately

150ºC and the thermal shutdown circuit is enabled (TSHUT_ENA = 1; TSHUT_OPDIS = 1) the

speaker and headphone amplifiers (LOUT, ROUT, SPKP, SPKN, OUT3 and OUT4) will be disabled.

TSHUT_ENA must be set to 1 to enable the temperature sensor when using the TSHUT_OPDIS

thermal shutdown function. The output of the temperature sensor can also be output to the GPIO

pins.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

TSHUT_ENA

(rw)

Thermal Sensor Enable

0 = Thermal sensor disabled

1 = Thermal sensor enabled

R2 (02h)

TSHUT_OPDIS

(rw)

Thermal Shutdown Enable

(Requires thermal sensor to be

enabled)

0 = Thermal shutdown disabled

1 = Thermal shutdown enabled

Table 35 Thermal Shutdown

When the speaker driver is operating in class AB mode the internal power dissipation of the WM8959

is likely to be significantly higher than when operating in class D mode.

Note: To prevent potential pops and clicks THSUT_ENA and TSHUT_OPDIS need to be configured

while the speaker and headphone outputs are off, i.e. LOUT_ENA, ROUT_ENA, OUT3_ENA,

OUT4_ENA and SPK_ENA are 0 (see also Table 70).

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