MC34118 Unisonic Technologies, MC34118 Datasheet - Page 12

• Manufacturer Part Number: MC34118
• Description: Voice Switched Speaker Phone Circuit
• Manufacturer: Unisonic Technologies

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UTC MC34118 LINEAR INTEGRATED CIRCUIT
POWER SUPPLY, VB, and CHIP DISABLE
operation possible down to 2.8 volts. The output voltage at VB( Pin 15) is ~(Vcc-0.7)/2, and provides the AC ground
for the system. The output impedance at VB is ~400Ω and in conjunction with the external capacitor at VB, forms a
low pass filter for power supply rejection. The choice of capacitor is application dependent based on whether the
circuit is powered by the telephone line or power supply. Since VB biases the microphone and hybrid amplifiers, the
amount of supply rejection at their outputs is directly related to the rejection at VB, as well as their respective gains.
The Chip Disable(Pin 3) permits powering down the IC to conserve power and/or for muting purposes. With CD<0.8
volts., normal operation is in effect. With CD>2 volts. and <Vcc, the IC is powered down. In the powered down mode,
the microphone and the hybrid amplifiers are disabled, and their outputs go to a high impedance state. Additionally,
the bias is removed from the level detectors. The bias is not removed from the filter( Pin 1, 2), the attenuators( Pin 8,
9, 21, 22), or from Pins 13, 14, and 15( the attenuators are disabled, however, and will not pass a signal impedance
at CD is typically 90kΩ, has a threshold of ~1.5 volts., and the voltage at this pin must be kept within the range of
ground and Vcc). If CD is not used, the pin should be grounded.
UTC
The power supply voltage at Vcc( Pin 4) is to be between 3.5 and 6.5 volts. for normal operation, with reduced
UNISONIC TECHNOLOGIES CO., LTD.
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