MC34119
DESIGN GUIDELINES
Figure 1. Turn–On Time versus C1, C2 at Power–On
General
The MC34119 is a low power audio amplifier capable of
360
low voltage operation (V
= 2.0 V minimum) such as that
CC
encountered in line–powered speakerphones. The circuit
300
provides a differential output (V –V ) to the speaker to
O1 O2
maximize the available voltage swing at low voltages. The
differential gain is set by two external resistors. Pins FC1 and
FC2 allow controlling the amount of power supply and noise
rejection, as well as providing alternate inputs to the
amplifiers. The CD pin permits powering down the IC for
muting purposes and to conserve power.
C1 = 5.0 µF
240
180
120
C1 = 1.0
4.0
µF
60
0
Amplifiers
V
switching from
CC
Referring to the block diagram, 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
0 V to 6.0 V
0
2.0
6.0
8.0
10
C2, CAPACITANCE (µF)
closed loop gain is set by external resistor R and R . The
f
i
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
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 MC34119 is enabled for normal
operation. When Pin 1 is at a Logic “1” (2.0 V to V
V), the
CC
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 kΩ. The power supply current (when disabled) is
shown in Figure 15.
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.
below V , at the maximum current. See Figures 18 and 19
CC
for V
and V
curves.
OL
OH
The output dc offset voltage (V –V ) is primarily a
function of the feedback resistor (R ), and secondarily due to
f
O1 O2
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.
Both times are independent of C1, C2, and V
.
CC
Amplifier #1’s bias current, however, flows out of V (Pin 4)
in
When the MC34119 is disabled, the voltages at FC1 and
and through R , forcing V
to shift negative by an amount
is shifted positive an equal amount.
O2
f
O1
FC2 do not change as they are powered from V . The
CC
outputs,V andV ,changetoahighimpedancecondition,
equal to [R × I ]. V
IB
f
O1
O2
The output offset voltage, specified in the Electrical
Characteristics, is measured with the feedback resistor
shown in the Typical Application Circuit, and therefore takes
into account the bias current as well as internal offset
voltages of the amplifiers. The bias current is constant with
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 V
and Ground.
CC
Power Dissipation
respect to V
.
Figures 8 to 10 indicate the device dissipation (within the
IC) for various combinations of V , R , and load power. The
maximum power which can safely be dissipated within the
MC34119 is found from the following equation:
CC
CC
L
FC1 and FC2
Power supply rejection is provided by the capacitors (C1
and C2 in the Typical Application 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 4 to 7. 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
P
= (140°C – T )/θ
A
D
JA
where T is the ambient temperature; and θ is the package
A
JA
thermal resistance (100°C/W for the standard DIP package,
and 180°C/W for the surface mount package.)
The power dissipated within the MC34119, in a given
application, is found from the following equation:
2
)
P
= (V
x I ) + (I
CC CC RMS
x V ) – (R x I
D
CC
L
RMS
Electrical Characteristics as R
and R ).
FC1
FC2
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 kΩ resistors. The graph of Figure 1 indicates the
where I
CC
is obtained from Figure 15; and I
is the RMS
RMS
current at the load; and R is the load resistance.
L
Figures 8 to 10, along with Figures 11 to 13 (distortion
curves), and a peak working load current of ±200 mA, define
the operating range for the MC34119. The operating range is
further defined in terms of allowable load power in Figure 14
for loads of 8.0 Ω, 16 Ω and 32 Ω. The left (ascending) portion
turn–on time upon application of V
of +6.0 V. The turn–on
CC
= 3.0 V, and ≈20% less for
time is ≈60% longer for V
CC
= 9.0 V. Turn–off time is <10 µs upon removal of V
V
.
CC
CC
4
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