LP3950 Datasheet, PDF (24/38 Pages) National Semiconductor (TI) – Color LED Driver with Audio Synchronizer

LP3950
SNVS331C – NOVEMBER 2004 – REVISED APRIL 2013
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The digitized input signal has a DC component that is removed by the digital DC REMOVER (-3 dB @ 400 Hz).
The automatic GAIN CONTROL adjusts the input signal to suitable range automatically. User can disable AGC
and the gain can be set manually with PROGRAMMABLE GAIN. The LP3950 has two audio synchronization
modes: amplitude and frequency. For amplitude based synchronization the PEAK DETECTION method is used.
For frequency based synchronization the three-way crossover FILTER separates high pass, low pass and band
pass signals. For both modes, a predefined lookup table (LUT) is used to match the audio visual effect. The
MODE SELECTOR selects the synchronization mode. Reaction speed can be selected using INTEGRATOR
speed variables. Finally PWM GENERATOR sets the driver FETs duty cycles.
Symbol
Zin
A_{IN_SINGLE}
A_{IN_DIFF}
f_{3 dB}
Table 4. Audio Synchronization Characteristics
Parameter
Input Impedance of AD1, AD2, ASE pins
Audio Input Level Range (peak-to-peak),
Single Ended Audio
Audio Input Level Range (peak-to-peak),
Differential Audio
Crossover Frequencies (−3 dB)
Narrow Frequency Response
Wide Frequency Response
Conditions
Low Pass
Band Pass
High Pass
Low Pass
Band Pass
High Pass
Min
Typ
200
500
0.1
0.1
0.5
1.0 and 1.5
2.0
1.0
2.0 and 3.0
4.0
Max
V_DDA −0.1
V_DDA −0.1
Units
kΩ
V
V
kHz
CONTROL OF AUDIO SYNCHRONIZATION
The following table describes the controls required for audio synchronization. Note that these controls are
functional when using serial interface (I²C or SPI) for device control. Also LP3950 audio synchronization
functionality is illustrated in Figure 27.
EN_SYNC
SYNC_MODE
MODE_CTRL[1:0]
EN_AGC
GAIN_SEL[2:0]
INPUT_SEL[1:0]
SPEED_CTRL[1:0]
Table 5. Audio Synchronization Control
Audio synchronization enabled. Set EN_SYNC = 1 to enable audio synchronization or 0 to disable.
Synchronization mode selector. Set SYNC_MODE = 0 for amplitude synchronization. Set SYNC_MODE
= 1 for frequency synchronization.
See below: Mode control
Automatic gain control. Set EN_AGC = 1 to enable automatic control or 0 to disable. When EN_AGC is
disabled, the audio input signal gain value is defined by GAIN_SEL.
Input signal gain control. Gain has a range from 0 dB to 21 dB with 3 dB steps:
[000] ... 0 dB
[011] ... 9 dB
[110] ... 18 dB
[001] ... 3 dB
[100] ... 12 dB
[111] ... 21 dB
[010] ... 6 dB
[101] ... 15 dB
[00] ... Single ended input signal, ASE.
[01] ... Differential input signal, AD1 and AD2.
[10] ... Stereo input or single ended and differential input signal.
Note: Sum of input signals divided by 2.
[11] ... No input
Please see Figure 24 for wiring.
Control for speed of the mapping. Sets the reaction speed (or "sampling rate") for the audio input signal:
[00] ... FASTEST
[01] ... FAST
[10] ... MEDIUM
[11] ... SLOW
In the amplitude mode f_MAX = 3.8 Hz, in the frequency mode f_MAX = 7.6 Hz.
24
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