WM8746
Production Data
DECOUPLING APPLICATIONS INFORMATION
SUPPLY PINS DESCRIPTION
PIN
1
NAME
DVDD
DGND
AVDD2
CAP
TYPE
Supply
DESCRIPTION
Digital Positive Supply.
Digital GND
11
15
16
20
24
28
Supply
Supply
Analogue Positive DAC Reference
Analogue Internal Mid-Rail Reference De-Coupling Point
Analogue GND
Analogue output
Supply
AGND1
AGND2
AVDD1
Supply
Analogue GND
Supply
Analogue VDD
DC ELECTRICAL CHARACTERISTICS
PARAMETER
SYMBOL
TEST CONDITIONS
AVDD = 5V
MIN
TYP
58
MAX
UNIT
mA
Analogue supply current
Digital supply current
Analogue supply current
Digital supply current
DVDD = 5V
22
mA
AVDD = 3.3V
DVDD = 3.3V
57
mA
11
mA
For proper decoupling, 0.1µF surface-mount ceramic capacitors are recommended for AVDD1,
AVDD2, DVDD and CAP. Also recommended are 10µF capacitors for AVDD, DVDD and CAP.
These are a general guideline and are dependent on the amount of noise present in the system.
If there is excessive noise on the supply, such as may be present in a commercial DVD receiver with
motors and switching amplifiers, additional filtering will be required. The supply AVDD2 is the
reference voltage for the DAC. It has no supply noise rejection, so any noise on this pin will affect the
DAC outputs. There is not much current drawn on this supply pin. Supply AVDD1 does have supply
rejection and draws most of the analogue supply current.
DECOUPLING EXAMPLES
Figure 25 Decoupling Example 1
In Figure 25, there is a single analogue supply that is fairly noisy. The AVDD1 and DVDD pins can
tolerate this, but the AVDD2 needs additional filtering. The schematic illustrates a suitable solution.
March 2006, PD Rev 4.0
29
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
