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MC34119P bảng dữ liệu(PDF) 4 Page - Freescale Semiconductor, Inc |
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MC34119P bảng dữ liệu(HTML) 4 Page - Freescale Semiconductor, Inc |
4 / 12 page MC34119 4 MOTOROLA ANALOG IC DEVICE DATA DESIGN GUIDELINES General The MC34119 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 ≥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 18 and 19 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 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 Ω 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 = 9.0 V. Turn–off time is <10 µs upon removal of VCC. C2, CAPACITANCE ( µF) Figure 1. Turn–On Time versus C1, C2 at Power–On 360 300 240 180 120 60 0 0 2.0 4.0 6.0 8.0 10 C1 = 5.0 µF C1 = 1.0 µF VCC switching from 0 V to 6.0 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 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 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. Both times are independent of C1, C2, and VCC. When the MC34119 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. Power Dissipation Figures 8 to 10 indicate the device dissipation (within the IC) for various combinations of VCC, RL, and load power. The maximum power which can safely be dissipated within the MC34119 is found from the following equation: PD = (140°C – TA)/θJA where TA is the ambient temperature; and θJA is the package 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: PD = (VCC x ICC) + (IRMS x VCC) – (RL x IRMS2) where ICC is obtained from Figure 15; and IRMS is the RMS current at the load; and RL is the load resistance. 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 |
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