LP3950 Datasheet, PDF (29/31 Pages) National Semiconductor (TI) – Color LED Driver with Audio Synchronizer

Typical Applications (Continued)
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There may be cases where the audio input signal going into the LP3950 is too weak for audio synchronization. This figure
presents a single-supply inverting amplifier connected to the ASE input for audio signal amplification. The amplification is +20 dB,
which is well enough for 20 mV_p-p audio signal. Because the amplifier (LMV321) is operating in single supply voltage, a voltage
divider using R₃ and R₄ is implemented to bias the amplifier so the input signal is within the input common-mode voltage range
of the amplifier. The capacitor C₄ is placed between the inverting input and resistor R₁ to block the DC signal going into the audio
signal source. The values of R₁ and C₄ affect the cutoff frequency, f_c = 1/(2*Pi*R₁*C₄), in this case it is around 160 Hz. As a result,
the LMV321 output signal is centered around mid-supply, that is V_DD/2. The output can swing to both rails, maximizing the
signal-to-noise ratio in a low voltage system
FIGURE 24. Backlight and Keypad LEDs Controlled by the Pattern Generator - Funlight LEDs Controlled by Audio
Synchronization
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