U4083B-AFP datasheet(2/11 Pages) TEMIC

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U4083B

TELEFUNKEN Semiconductors

Rev. A2, 07-Apr-97

Preliminary Information

2 (11)

Pin Description

94 8022

V i

FC1

FC2

GND

VO1

VO2

V S

Figure 2. Pinning

Symbol

Function

Chip disable

FC2

Filtering, power supply rejection

FC1

Filtering, power supply rejection

Amplifier input

VO1

Amplifier output 1

Voltage supply

GND

Ground

VO2

Amplifier output 2

Functional Description

Including External Circuitry

Pin 1: Chip disable

* digital input (CD)

Pin 1 (chip disable) is used to power down the IC to con-

serve power or muting or both.

Input impedance at pin 1 is typically 90 k

Logic 0 < 0.8 V

IC enabled (normal operation)

Logic 1 > 2 V

IC disabled

Figure 15 shows 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

ton = 12 to 15 ms

turn-off time

toff

v 2 ms

They are independent of C1, C2 and VS.

Voltages at Pins 2 and 3 are supplied from VS and there-

fore do not change when the U4083B is disabled.

Outputs– VO1 (Pin 5) and VO2 (Pin 8) –turn to a high im-

pedance 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 be-

tween the supply voltage, Vs, and Ground.

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

(figures 4 to 7). 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 looking into 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 capaci-

tors are charged up through the internal resistors (50 k

and 125 k

W) as shown in the block diagram.

Figure 1 shows turn-on time versus C2 at VS = 6 V, for two

different C1 values.

Turn-on time is 60% longer when VS = 3 V and 20%

shorter when VS = 9 V.

Turn-off time is less than 10

Pin 4: Amplifier input

Pin 5: Amplifier output 1 VO1

Pin 8: Amplifier output 2 VO2

There are two identical operational amplifiers. Amp.1 has

an open loop gain

w 80 dB at 100 Hz (figure 2), whereas

the closed loop gain is set by external resistors, Rf and Ri

(figure 3). The amplifier is unity gain stable, and has a

unity gain frequency of approximately 1.5 MHz. A closed

loop gain of 46 dB is recommended for a frequency range

of 300 to 3400 Hz (voice band). Amp.2 is internally set

to a gain of –1.0 (0 dB). The outputs of both amplifiers are

capable of sourcing and sinking a peak current of 200 mA.

Output voltage swing is between 0.4 V and Vs – 1.3 V at

maximum current (figures 18 and 19).

The output dc offset voltage between Pins 5 and 8 (VO1

– VO2) is mainly a function of the feedback resistor, Rf,

because the input offset voltage of the two amplifiers

generally neutralize each other.

Bias current of Amp. 1 which is constant with respect to

Vs, however flows out of Pin 4 (Vi) and through Rf,

forcing V01 to shift negative by an amount equal to Rf IIB

and VO2 positive to an equal amount.

The output offset voltage specified in the electrical char-

acteristics is measured with the feedback resistor

(Rf = 75 k

W) shown in typical application circuit. It takes

into account bias current as well as internal offset voltages

of the amplifiers.

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