U4083B Datasheet, PDF (3/16 Pages) TEMIC Semiconductors – Low-Power Audio Amplifier for Telephone Applications

U4083B
3. Functional Description Including External Circuitry
3.1 Pin 1: Chip Disable Digital Input (CD)
Pin 1 (chip disable) is used to power down the IC to conserve power or mute the IC or both.
Input impedance at Pin 1 is typically 90 kΩ.
• Logic 0 < 0.8V IC enabled (normal operation)
• Logic 1 > 2V IC disabled
Figure 8-15 on page 12 shows the power supply current diagram. The change in differential gain
from normal operation to muted operation (muting) is more than 70 dB.
Switching characteristics are as follows:
• Turn-on time
t_on = 12 ms to 15 ms
• Turn-off time
t_off ≤2 µs
They are independent of C₁, C₂ and V_S.
Voltages at Pins 2 and 3 are supplied from V_S and, therefore, do not change when the U4083B
is disabled. The outputs, V_O1 (Pin 5) and V_O2 (Pin 8), turn to a high impedance condition by
removing the signal from the speaker.
When signals are applied from an external source to the outputs (disabled), they must not
exceed the range between the supply voltage, V_S, and ground.
3.2 Pins 2 and 3: Filtering, Power Supply Rejection
Power supply rejection is provided by capacitors C₁ and C₂ at Pin 3 and Pin 2, respectively. C₁ is
dominant at high frequencies whereas C₂ is dominant at low frequencies (Figure 8-4 on page 8
to Figure 8-7 on page 9). The values of C₁ and C₂ depend on the conditions of each application.
For example, a line-powered speakerphone (telephone amplifier) will require more filtering than
a system powered by regulated power supply.
The amount of rejection is a function of the capacitors and the equivalent impedance at Pin 3
and Pin 2 (see electrical characteristic equivalent resistance, R).
Apart from filtering, capacitors C₁ and C₂ also influence the turn-on time of the circuit at power
up, since the capacitors are charged up through the internal resistors (50 kΩ and 125 kΩ) as
shown in the block diagram.
Figure 8-1 on page 7 shows the turn-on time versus C₂ at V_S = 6V, for two different C₁ values.
The turn-on time is 60% longer when V_S = 3V and 20% shorter when V_S = 9V.
The turn-off time is less than 10 µs.
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