WM8711 Wolfson Microelectronics Ltd., WM8711 Datasheet - Page 15

• Manufacturer Part Number: WM8711
• Description: Internet Audio DAC With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8711
DEVICE OPERATION
WOLFSON MICROELECTRONICS LTD
The recommended external components required to complete the application are shown in Figure 11.
Figure 11 Headphone Output Application Drawing
Recommended values are C1 = 220uF (10V electrolytic), R1 = 47KOhms
C1 forms a DC blocking capacitor to isolate the dc of the HPOUT from the headphones. R1 form a
pull down resistor to discharge C1 to prevent the voltage at the connection to the headphones from
rising to a level that may damage the headphones. L1 (optional) forms a phase shifting network with
the headphone load aiding overall performance, and increasing the protection of the WM8711
headphone amplifier from potentially destructive externally applied electrostatic discharge events.
DEVICE RESETTING
The WM8711 contains a power on reset circuit that resets the internal state of the device to a known
condition. The power on reset is applied as DCVDD powers on and released only after the voltage
level of DCVDD crosses a minimum turn off threshold. If DCVDD later falls below a minimum turn on
threshold voltage then the power on reset is re-applied. The threshold voltages and associated
hysteresis are shown in the Electrical Characteristics table.
The user also has the ability to reset the device to a known state under software control as shown in
the table below.
When using the software reset. In 3-wire mode the reset is applied on the rising edge of CSB and
released on the next rising edge of SCLK. In 2-wire mode the reset is applied for the duration of the
ACK signal (approximately 1 SCLK period, refer to Figure 20).
CLOCKING SCHEMES
In a typical digital audio system there is only one central clock source producing a reference clock to
which all audio data processing is synchronised. This clock is often referred to as the audio system’s
Master Clock. To allow WM8711 to be used in a centrally clocked system, the WM8711 is capable of
either generating this system clock itself or receiving it from an external source as will be discussed.
For applications where it is desirable that the WM8711 is the system clock source, then clock
generation is achieved through the use of a suitable crystal connected between the XTI/MCLK input
and XTO output pins (see CRYSTAL OSCILLATOR section).
Table 5 Software Control of Reset
0001111
Reset Register
REGISTER
ADDRESS
HPOUT
8:0
BIT
RESET
LABEL
C1
not reset
DEFAULT
AGND
R1
Reset Register
Writing 00000000 to register resets
device
DESCRIPTION
PP Rev 1.2 November 2000
AGND
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