WM8746

Production Data

w

March 2006, PD Rev 4.0

29

DECOUPLING APPLICATIONS INFORMATION

SUPPLY PINS DESCRIPTION

PIN

NAME

TYPE

DESCRIPTION

1

DVDD

Supply

Digital Positive Supply.

11

DGND

Supply

Digital GND

15

AVDD2

Supply

Analogue Positive DAC Reference

16

CAP

Analogue output

Analogue Internal Mid-Rail Reference De-Coupling Point

20

AGND1

Supply

Analogue GND

24

AGND2

Supply

Analogue GND

28

AVDD1

Supply

Analogue VDD

DC ELECTRICAL CHARACTERISTICS

PARAMETER

SYMBOL

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Analogue supply current

AVDD = 5V

58

mA

Digital supply current

DVDD = 5V

22

mA

Analogue supply current

AVDD = 3.3V

57

mA

Digital supply current

DVDD = 3.3V

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.