AD1845 datasheet(36/40 Pages) AD

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AD1845

–36–

REV. C

Analog Devices recommends that all digital pins be driven from

the same supply. A common technique to achieve maximum

performance is to use a +5 V regulator to power the analog side

of the codec from the PCs +12 V supply line, while the standard

PC +5 V supply line powers the entire digital side of the codec.

The separate supplies provide noise isolation for the analog side

of the codec, and maximize performance of the AD1845.

ANALOG

GROUND

PLANE

DIGITAL

GROUND

PLANE

AD1845

PLCC

GNDD

R_AUX2

R_FILT

ANALOG

GROUND

PLANE

DIGITAL

GROUND

PLANE

AD1845

TQFP

R_FILT

Figure 36. Recommended Ground Plane

COMPATIBILITY WITH CS4231

1. The CS4231 requires a 1000 pF NPO type capacitor on

Pins 26 and 31. The AD1845 requires a 1

µF capacitor on

filter Pins 26 and 31. To achieve compatibility with the

AD1845, use pad spacing that will accommodate either

1000 pF NPO capacitors for the CS4231 and the CS4248

or the 1

µF capacitors for the AD1845.

The AD1845 requires the input antialiasing filters for the

ADCs (refer to Figures 27 and 28). The CS4231 can use

the same filters with no degradation in performance. For

compatibility it is suggested that the filters be added.

The CS4231 does not require the power pins (VDD) 24,

45, and 54, or the ground pins (GNDD) 25, and 44. It is

suggested that the appropriate power/ground pin connec-

tions be made. This will not affect the performance of the

CS4231.

The CS4231 does not provide software programmable

power-down modes.

The CS4231 does not have the ability to mix the MIC

input with the DAC output.

6. The CS4231 does not contain a Variable Sample Fre-

quency Generator and cannot change sample rates “on the

fly.” The CS4231 and CS4248 require entering MCE to

change the sample rate. The AD1845 can change the

sample rate without entering MCE. The AD1845’s 50,000

selectable sample rates are not available on the CS4231.

The Variable Sample Frequency Generator reduces clicks

and pops encountered in many game applications.

7. The CS4231 requires two crystal inputs, 24.575 MHz and

16.9344 MHz. The AD1845 requires only one input of

24.576 MHz or can be driven from OSC or other exter-

nal clocks.

8. The CS4231 does not contain the INITD bit.

9. The CS4231 minimum RIN = 20 k

Ω. The AD1845 mini-

mum input resistance is 10 k

Ω.

10. The AD1845 does not include hardware for compressing

and decompressing ADPCM data. Analog Devices offers

Windows based software applets for using ADPCM for-

mats with the AD1845.

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