WM8351CGEB/RV WOLFSON [Wolfson Microelectronics plc], WM8351CGEB/RV Datasheet - Page 102

• Manufacturer Part Number: WM8351CGEB/RV
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM8351
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Whenever an analogue input/output is disabled, it remains connected to AVDD/2 through a resistor.
This helps to prevent pop noise when the output is re-enabled. The resistance between the voltage
buffer and the output pins can be controlled using the VROI control bits. The default impedance is
low, so that any capacitors on the outputs can charge up quickly at start-up. If high impedance is
desired for disabled outputs, VROI can then be set to 1, increasing the resistance to about 30k.
There are individual VROI bits for each output or output pair. This allows matching of the rise times of
the outputs if they are driving different capacitors. Using the small resistance with a capacitor for
headphone outputs (typically 220uF) and the larger resistance with a line load capacitance (10uF for
example); will allow both sets of outputs to power up in around the same time, around 200ms.
Table 52 Disabled Outputs to VREF Resistance
A dedicated buffer is available for tying off unused analogue I/O pins as shown below. This buffer can
be enabled using the VBUF_ENA register bit.
13.12.5 UNUSED ANALOGUE INPUTS/OUTPUTS
R8 (08h)
Power Mgmt
1
R76 (4Ch)
Output
Control
REGISTER
ADDRESS
BIT
13
10
11
8
9
VBUF_ENA
OUT1_VROI
OUT2_VROI
OUT3_VROI
OUT4_VROI
LABEL
DEFAULT
0
0
0
0
0
Forces ON the tie-off amplifiers
0 = Disabled
1 = Enabled
VREF (AVDD/2) to OUT1L/OUT1R
resistance
0 = approx 500
1 = approx 30 k
VREF (AVDD/2) to OUT2L/OUT2R
resistance
0 = approx 500
1 = approx 30 k
VREF (AVDD/2) to OUT3 resistance
0 = approx 500
1 = approx 30 k
VREF (AVDD/2) to OUT4 resistance
0 = approx 500
1 = approx 30 k
DESCRIPTION
PD, April 2012, Rev 4.5
Production Data
102