Audio Synchronization

The LED1 output can be synchronized to incoming audio

signal with Audio Synchronization feature. Audio Synchroni-

zation synchronizes LED1 based on input signal’s peak am-

plitude. Programmable gain and automatic gain control func-

tion are also available for adjustment of input signal

amplitude to light response. Control of LED1 brightness

refreshing frequency is done with four different frequency

configurations. The digitized input signal has a DC compo-

nent that is removed by a digital DC-remover. The DC-

remover is a high-pass filter where corner frequency is user

selectable by using DC_FREQ bit. LP55271 has 2-channel

audio (stereo) input for audio synchronization, as shown in

the figure below. The inputs accept signals in the range of 0V

to 1.6V peak-to-peak and these signals are mixed into a

single wave so that they can be filtered simultaneously.

LP55271 audio synchronization is mainly done digitally and

it consists following signal path blocks (see figure below).

•

Input buffer

•

AD converter

•

Automatic Gain Control (AGC) and manually program-

mable gain

•

Peak detector

Automatic Gain Control (AGC) adjusts the input signal to

suitable range automatically. User can disable AGC and the

gain can be set manually with programmable gain. Audio

synchronization is based on peak detection method.

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Audio Synchronization Input Electrical Parameters

Symbol

Parameter

Conditions

Min

Typ

Max

Units

Z

IN

Input Impedance of

ASE1, ASE2

10

15

k

Ω

A

IN

ASE1, ASE2 Audio

Input Level Range

(peak-to-peak)

Min input level needs maximum gain;

Max input level for minimum gain.

0

1600

mV

CONTROL OF AUDIO SYNCHRONIZATION

The following table describes the controls required for audio synchronization. LED1 brightness control through serial interface is

not available when audio synchronization is enabled.

Audio Synchronization Control

EN_SYNC

Audio synchronization enabled. Set EN_SYNC=1to enable audio synchronization or 0 to disable.

EN_AGC

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

When EN_AGC is disabled, the audio input signal gain value is defined by GAIN_SEL.

GAIN_SEL[2:0]

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

SPEED_CTRL[1:0]

Control for refreshing frequency. Sets the typical refreshing rate for the LED1 output.

THRESHOLD[3:0]

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

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

DC_FREQ

Control for the high-pass filter corner frequency.

0=80Hz

1 = 510 Hz

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