GP34119 Datasheet, PDF (3/8 Pages) List of Unclassifed Manufacturers – LOW POWER AUDIO AMPLIFIER

ISSUED DATE :2005/02/18
REVISED DATE :
Pin Function Description
Symbol
Pin
Description
CD
1
Chip Disable-Digital input. A Logic “0” (<0.8V) sets normal operation. A Logic “1” (Њ2V) sets the
power down mode. Input impedance is nominally 90k .
FC2
2
A capacitor at this pin increases power supply rejection, and affects turn-on time. This pin can be left
open if the capacitor at FC1 is sufficient.
FC1
Analog ground for the amplifiers. A 1.0uF capacitor at this pin (with a 5.0uF capacitor at Pin 2)
3
provides (typically) 52dB of power supply rejection. Turn-on time of the circuit is affected by the
capacitor on this pin. This pin can be used as an alternate input.
Vin
VO1
VCC
GND
4
Amplifier input. This input capacitor and resistor set low frequency rolloff and input impedance. The
feedback resistor is connected to this pin and VO1.
5
Amplifier Output #1. The dc level is (VCC – 0.7)/2.
6
DC supply voltage (+2V to +16V) is applied to this pin.
7
Ground pin for the entire circuit.
VO2
8
Amplifier Output #2. This signal is equal in amplitude, but 180°out-of-phase with that at VO1.
The dc level is (VCC – 0.7)/2.
Typical Temperature Performance (-20к < TA < +70к)
Function
Input Bias Current (@ Vin)
Total Harmonic Distortion(VCC=6V, RL=32 Pout=125mW, f=1kHz)
Power Supply Current
(VCC=3V, RL= , CD=0V)
(VCC=3V, RL= , CD=2V)
Typical Change
±40
+0.003
-0.25
-0.03
Units
pA/к
%/к
uA/к
Design Guidelines
General
The GPC34119 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 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.
Amplifiers
Referring to the block diagram, the internal configuration consists of two identical operational amplifiers. Amplifier # 1 has an open loop
gain of Њ 80 dB (at fЉ 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(0dB).
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 with 1.3 V below VCC, at the maximum current. See Figures 17 and 18 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 swill 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 V01 to shift negative by an
amount equal to [Rf x 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 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 respect to VCC.
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 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 1 indicates the turn-on time upon application of VCC of + 6.0 V. The
turn-on time is 60% longer for VCC = 3.0 V, and 20% less for VCC = 9.0V. Turn-off time is < 10 us upon removal of VCC.
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