LA2806M Datasheet, PDF (6/11 Pages) Sanyo Semicon Device – Signal Processor and Power Amplifier IC for Telephone Answering Machines

LA2806M
IC Usage Notes
1) Control Inputs (pin 26 to 30)
Each control input is connected to V_REF through a 100 kΩ resistance. The control input threshold level is V_REF × 3/5.
2) Automatic Level Control (ALC)
The automatic level control circuit operates when the input signal is in the range between –64 dBV to –20 dBV. The output
saturation level is 500 mV rms.
3) Mute Circuit (pin 24)
The VOX. C/MUTE input controls the mute function.
When it goes HIGH, analog switch SW5 opens, switching off the power amplifier. The power amplifier output goes high
impedance and VOX (pin 25) goes LOW.
4) V/I Conversion
V/I conversion is performed in order to extract the recording current for DC bias. The conversion gain and the bias current
can be controlled by an external resistor connected to pin 1, and current that is equal to the pin 1 output current is output on
pin 2.
5) Playback Amplifier and Preamplifier Feedback Resistance
As the playback amplifier and preamplifier employ a zero-bias method, the amplifier’s output DC level (V_ODC) is determined
by the feedback resistance (R_NF) and the NF pin sink current (Ii = 15 µA).
V_ODC = V_BE + R_NF × Ii
V_BE 6 0.7 V
A feedback resistance of 100 kΩ is recommended for both the playback amplifier and the preamplifier to provide an output
DC level with sufficient output dynamic range.
6) Filter amplifier
A bandwidth-limiting filter is provided to restrict the VOX circuit input frequency. It can also be used as an inverting
amplifier. It has a center frequency of 800 Hz, a gain of 2 and a Q factor of 1.
Unit (resistance: Ω, capacitance: F)
7) Voice-operated Switch (VOX)
This switch detects whether anyone is speaking or not by detecting the level of the signal (V13) on the filter amplifier output
pin (pin 13).
V13 % –18 dBV ... Pin 25 low
The detection level is adjusted by inserting resistor R between TH (pin 23) and V_REF (pin 14).
Refer to the diagram below.
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