CS4297 datasheet(32/46 Pages) CIRRUS

32 / 46 page

DS242F5

CS4297

CrystalClear™ SoundFusion™ Audio Codec ’97

Miscellaneous Analog Signals

The AFILT1 and AFILT2 pins must have a 390 pF

NPO capacitor (must not be smaller than 390 pF) to

analog ground. These capacitors, along with an in-

ternal resistor, provide a single-pole low-pass filter

at the inputs to the ADCs. By placing these filters

at the input to the ADCs, low-pass filters at each

analog input pin are not necessary.

The REFFLT pin lowers the noise of the internal

voltage reference. A 1

µF (must not be greater than

µF) and 0.1 µF capacitor to analog ground should

be connected with a short, wide trace to this pin

(see Figure 10 in the Grounding and Layout section

for an example). No other connection should be

made, as any coupling onto this pin will degrade

the analog performance of the Codec. Likewise,

digital signals should be kept away from REFFLT

for similar reasons.

The Vrefout pin is typically 2.2 V and provides a

common mode signal for single-supply external

circuits. Vrefout only supports light DC loads and

should be buffered if AC loading is needed. For

typical use, a 0.1

µF in parallel with a 1 µF capaci-

tor should be connected to Vrefout.

Power Supplies

The power supplies providing analog power should

be as clean as possible to minimize coupling into

the analog section which could degrade analog per-

formance. The pins AVdd1 and AVdd2 supply

power to all the analog circuitry on the CS4297.

This 5 Volt analog supply should be generated

from a voltage regulator (7805 type) connected to a

+12 Volt supply. This helps isolate the analog cir-

cuitry from noise typically found on +5 V digital

supplies which power many digital circuits in a PC

environment. A typical voltage regulator circuit for

analog power using an MC78M05CDT is shown in

Figure 9.

The digital power pins DVdd1 and DVdd2 should

be connected to the same digital supply as the

AC’97 Controller’s AC-Link interface. Since the

digital interface on the CS4297 may operate at ei-

ther 3.3 V or 5 V, proper connection of these pins

will depend on the digital power supply of the

AC’97 Controller.

+12VD

AGND

DGND

+5VA

0.1µF

Y5V

10µF

ELEC

10µF

ELEC

MC78M05CDT

OUT

GND

0.1µF

Y5V

Figure 9. Voltage Regulator

CS4297 Datasheet(PDF) 32 Page - Cirrus Logic

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