LP3950SL datasheet(29/31 Pages) NSC

29 / 31 page

Typical Applications (Continued)

20129343

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 R

3 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 C

4 is placed between the inverting input and resistor R1 to block the DC signal going into the audio

signal source. The values of R

1 and C4 affect the cutoff frequency, fc = 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

LP3950SL 数据表(PDF) 29 Page - National Semiconductor (TI)