15k

ASE2

ADC

GAIN_SEL[2:0]

EN_AGC

PEAK

DETECTOR

ALED

CONTROL

HOLD

SPEED_CTRL[1:0]

THRESHOLD[3:0]

ASE1

15k

Threshold

&

AGC

LP55281

www.ti.com

SNVS458B – JUNE 2007 – REVISED JUNE 2007

CONTROL OF AUDIO SYNCHRONIZATION

The following table describes the controls required for audio synchronization. ALED brightness control through

serial interface is not available when audio synchronization is enabled.

Table 2. Audio Synchronization Control (Registers 0Dh and 0Eh)

GAIN_SEL[2:0]

Register 0Dh

Input signal gain control. Gain has a range from 0 dB to -46 dB.

Bits 7-5

[000] = 0 dB, [001] = -6 dB, [010] = -12 dB, [011] = -18 dB,

[100] = -24 dB, [101] = -31 dB, [110] = -37 dB, [111] = -46 dB

DC_FREQ

Register 0Dh

Control of the high-pass filter's corner frequency:

Bit 4

0 = 80 Hz

1 = 510 Hz

EN_AGC

Register 0Dh

Automatic gain control. Set EN_AGC = 1 to enable automatic control or 0

Bits 3

to disable. When EN_AGC is disabled, the audio input signal gain value is

defined by GAIN_SEL.

EN_SYNC

Register 0Dh

Audio synchronization enabled. Set EN_SYNC = 1 to enable audio

Bits 2

synchronization or 0 to disable.

SPEED_CTRL[1:0]

Register 0Dh

Control for refreshing frequency. Sets the typical refreshing rate for the

Bits 1-0

ALED output

[00] = FASTEST, [01] = 15 Hz, [10] = 7.6 Hz, [11] = 3.8 Hz

THRESHOLD[3:0]

Register 0Eh

Control for the audio input threshold. Sets the typical threshold for the

Bits 3-0

audio inputs signals. May be needed if there is noise on the audio lines.

Table 3. Audio Input Threshold Setting (Register 0Eh)

THRESHOLD[3:0]

Threshold Level, mV (typical)

0000

Disabled

0001

0.2

0010

0.4

...

...

1110

2.5

1111

2.7

Table 4. Typical Gain Values vs Audio Input Amplitude

Gain Value dB

0 to 10

0

0 to 20

-6

0 to 40

-12

1 to 85

-18

3 to 170

-24

5 to 400

-31

10 to 800

-37

20 to 1600

-46

Copyright © 2007, Texas Instruments Incorporated

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