AS3687 datasheet(40/55 Pages) AMSCO

40 / 55 page

AS3687/87XM

Datasheet

www.austriamicrosystems.com/AS3687

1v3-4

39 - 54

The internal circuit has the following functions:

Figure

29 – Audio controlled RGB LED internal circuit

CURR33/AUDIO_IN

Audio IN

1.25V

ADC

optional

adc_select

CURR30

CURR31

CURR32

other modes

curr3x_out

CURR1

CURR2

CURR6

other modes

curr126_out

audio_gain

-12dB...+30dB

aud_buf_on

Remove

Level

Detect /

Fadeout

AGC

Look

Table

audio_color

agc_ctrl

audio_speed

rgb_amplitude

The audio controlled LED block is enabled if any of the registers curr3x_out or curr126_out is not zero.

The audio input amplifier (enabled by aud_buf_on=1) is used to allow the attenuation (or amplification of the input

signal) and has the following parameters:

Table

15 – Audio input Parameters

Symbol

Parameter

Min

Typ

Max

Unit

Note

Vin

Input Voltage Range

2.5

Rin_min

min. Input Impedance

kΩ

at max. input gain (30dB)

When audio control RGB LED is active, the internal ADC is continuously running at a sample frequency of

45.5kHz. In this case the ADC cannot be used for any other purpose.

The input amplitude is mapped into different colors for RGB LED(s) or brightness for single color LED(s). The

mapping is controlled by the register audio_color. If audio_color = 000, then the mapping is done as follows:

Very low amplitudes are mapped to black, for higher amplitudes, the color smoothly transitions from blue, green,

cyan, yellow, red and eventually to white (for high input amplitudes). Otherwise the output is mapped to the

brightness of a single color.

7.6.1 AGC

The AGC is used to ‘compress’ the input signal and to attenuate very low input amplitude signals (this is

performed to ensure no light output for low signals especially for noisy input signals).

The AGC monitors the input signal amplitude and filters this amplitude with a filter with a short attack time, but a

long decay time (decay time depends on the register agc_ctrl). This amplitude measurement (represented by an

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