34119 datasheet(12/17 Pages) FREESCALE

12 / 17 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

34119

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The 34119 is a low power audio amplifier capable of low

voltage operation (VCC = 2.0 V minimum), such as that

encountered in line-powered speakerphones. The circuit

provides a differential output (VO1-VO2) to the speaker to

maximize the available voltage swing at low voltages. The

differential gain is set by two external resistors. Pins FC1 and

FC2 allow control of the amount of power supply and noise

rejection, as well as providing alternate inputs to the

amplifiers. The CD pin permits power down of the IC for

muting purposes and to conserve power.

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

AMPLIFIERS

Referring to the Internal Block Diagram on page 2, the

internal configuration consists of two identical operational

amplifiers. Amplifier #1 has an open loop gain of ≥80 dB (at

f ≤ 100 Hz), and the closed loop gain is set by external

resistor RF and RI. The amplifier is unity gain stable, and has

a unity gain frequency of approximately 1.5 MHz. In order to

adequately cover the telephone voice band (300 Hz to 3400

Hz), a maximum closed loop gain of 46 is recommended.

Amplifier #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. The outputs can typically

swing to within

≈0.4 V above ground, and to within ≈1.3 V

below VCC, at the maximum current. See Figures 20 and 21

for VOH and VOL curves.

The output dc offset voltage (VO1 - VO2) is primarily a

function of the feedback resistor (RF), and secondarily due to

the amplifiers’ input offset voltages. The input offset voltage

of the two amplifiers will generally be similar for a particular

IC, and therefore nearly cancel each other at the outputs.

Amplifier #1’s bias current, however, flows out of VIN (Pin 4)

and through RF, forcing VO1 to shift negative by an amount

equal to [RF ⋅ IIB]. VO2 is shifted positive an equal amount.

The output offset voltage, specified in the Electrical

Characteristics, is measured with the feedback resistor

shown in the Typical Applications Circuit, and therefore takes

into account the bias current as well as internal offset

voltages of the amplifiers. The bias current is constant with

respect to VCC.

FC1 AND FC2

Power supply rejection is provided by the capacitors (C1

and C2 in the Typical Applications Circuit) at FC1 and FC2.

C2 is somewhat dominant at low frequencies, while C1 is

dominant at high frequencies, as shown in the graphs of

Figures 6 to 9. The required values of C1 and C2 depend on

the conditions of each application. A line powered

speakerphone, for example, will require more filtering than a

circuit powered by a well regulated power supply. The

amount of rejection is a function of the capacitors, and the

equivalent impedance looking into FC1 and FC2 (listed in the

Electrical Characteristics as RFC1 and RFC2).

In addition to providing filtering, C1 and C2 also affect the

turn-on time of the circuit at power-up, since the two

capacitors must charge up through the internal 50 k and

125 k

. resistors. The graph of Figure 29 indicates the turn-on

time upon application of VCC of +6.0 V. The turn-on time is

≈60% longer for V

CC = 3.0 V, and ≈20% less for VCC = 9.0 V.

Turn-off time is <10

µs upon removal of V

CC.

Figure 29. Turn-On Time versus C1 and C2 at Power-On

CHIP DISABLE

The Chip Disable (Pin 1) can be used to power down the

IC to conserve power, or for muting, or both. When at a Logic

“0” (0 V to 0.8 V), the 34119 is enabled for normal operation.

When Pin 1 is at a Logic “1” (2.0 V to VCC V), the IC is

disabled. If Pin 1 is open, that is equivalent to a Logic “0,”

although good design practice dictates that an input should

never be left open. Input impedance at Pin 1 is a nominal

90 k

Ω. The power supply current (when disabled) is shown in

Figure 17.

Muting, defined as the change in differential gain from

normal operation to muted operation, is in excess of 70 dB.

The turn-off time of the audio output, from the application of

the CD signal, is <2.0

µs, and turn-on time is 12 ms-15 ms.

Both times are independent of C1, C2, and VCC.

When the 34119 is disabled, the voltages at FC1 and FC2

do not change as they are powered from VCC. The outputs,

VO1 and VO2, change to a high impedance condition,

removing the signal from the speaker. If signals from other

sources are to be applied to the outputs (while disabled), they

must be within the range of VCC and Ground.

C2, CAPACITANCE (

µF)

360

300

240

180

120

2.0

4.0

6.0

8.0

C1=5.0

µF

C1=1.0

VCC switching from

0Vto6.0 V

µF

34119 Datasheet(PDF) 12 Page - Freescale Semiconductor, Inc

34119 Datasheet(HTML) 12 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Datasheet Download

Link URL