AD1885JST Analog Devices Inc, AD1885JST Datasheet - Page 26

• Manufacturer Part Number: AD1885JST
• Description: IC AUDIO CODEC AC'97 48-LQFP
• Manufacturer: Analog Devices Inc
• Series: SoundMAX®r
• Type: Audio Codec '97r

Specifications of AD1885JST

• Rohs Status: RoHS non-compliant
• Data Interface: Serial
• Resolution (bits): 16 b
• Number Of Adcs / Dacs: 2 / 2
• Sigma Delta: Yes
• Dynamic Range, Adcs / Dacs (db) Typ: 87 / 90
• Voltage - Supply, Analog: 4.75 V ~ 5.25 V
• Voltage - Supply, Digital: 3.15 V ~ 3.45 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP

AD1885
PC_BEEP INPUT CONNECTIONS
The recommended PC_BEEP input circuit is shown below. Under most cases the PC_BEEP signal should be attenuated, filtered and
then ac-coupled into the Codec.
GROUNDING AND LAYOUT
To reduce noise and emissions, Analog Devices recommends a split ground plane as shown in Figure 18. The purpose of splitting
the ground plane is to create a low noise analog area that is somewhat isolated from the digital ground current noise generated
by the system’s logic. All the analog circuitry should be placed on the analog ground plane area.
For reference purposes, and to return power supply currents, the analog and digital ground planes must be connected at some point,
ideally a small bridge under or near the Codec should be provided. A 0 Ω resistor or a ferrite bead should also be considered since
these allow some flexibility in optimizing the layout to meet EMC requirements.
ANALOG POWER SUPPLY
To minimize audio noise, the Codec analog power supply (AVDD) should be well decoupled and regulated. In PC systems it is rec-
ommended that the analog supply be derived from the 12 V PC power supply using a localized linear voltage regulator. Preferably,
the analog power supply should be connected to the Codec’s analog section using a ferrite bead.
If a power plane layer is being used in the system design, it is recommended that the analog power plane for the Codec also be split
(mirroring the analog ground plane). In this case, the analog power supply ferrite bead should bridge the isolation trench, close to
the Codec location.
PC_BEEP (FROM ICH)
ISOLATION
GROUND PLANE
TRENCH
DIGITAL
PIN 1
AD1885
CONNECT SPLIT GROUND
PLANES AT OR NEAR CODEC.
GROUND PLANE
ANALOG
TO CODEC PC_BEEP INPUT