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TDA7375AH データシート(PDF) 9 Page - STMicroelectronics |
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TDA7375AH データシート(HTML) 9 Page - STMicroelectronics |
9 / 14 page High Application Flexibility The availability of 4 independent channels makes it possible to accomplish several kinds of applica- tions ranging from 4 speakers stereo (F/R) to 2 speakers bridge solutions. In case of working in single ended conditions the polarity of the speakers driven by the inverting amplifier must be reversed respect to those driven by non inverting channels. This is to avoid phase inconveniences causing sound alterations especially during the reproduc- tion of low frequencies. Easy Single Ended to Bridge Transition The change from single ended to bridge configu- rations is made simply by means of a short circuit across the inputs, that is no need of further exter- nal components. Gain Internally Fixed to 20dB in Single Ended, 26dB in Bridge Advantages of this design choice are in terms of: components and space saving output noise, supply voltage rejection and dis- tortion optimization. Silent Turn On/Off and Muting/Stand-by Func- tion The stand-by can be easily activated by means of a CMOS level applied to pin 7 through a RC filter. Under stand-by condition the device is turned off completely (supply current = 1 µA typ.; output at- tenuation= 80dB min.). Every ON/OFF operation is virtually pop free. Furthemore, at turn-on the device stays in muting condition for a time determined by the value as- signed to the SVR capacitor. While in muting the device outputs becomes in- sensitive to any kinds of signal that may be pre- sent at the input terminals. In other words every transient coming from previous stages produces no unplesant acoustic effect to the speakers. OUTPUT STAGE The fully complementary output stage was made possible by the development of a new compo- nent: the ST exclusive power ICV PNP. A novel design based upon the connection shown in fig. 20 has then allowed the full exploitation of its possibilities. The clear advantages this new approach has over classical output stages are as follows: Rail-to-Rail Output Voltage Swing With No Need of Bootstrap Capacitors. The output swing is limited only by the VCEsat of the output transistors, which are in the range of 0.3 Ω (Rsat) each. Classical solutions adopting composite PNP- NPN for the upper output stage have higher saturation loss on the top side of the waveform. This unbalanced saturation causes a signifi- cant power reduction. The only way to recover power consists of the addition of expensive bootstrap capacitors. Absolute Stability Without Any External Compensation. Referring to the circuit of fig. 20 the gain VOut/VIn is greater than unity, approximately 1+ R2/R1. The DC output (VCC/2) is fixed by an auxiliary amplifier common to all the channels. By controlling the amount of this local feedback it is possible to force the loop gain (A* β) to less than unity at frequency for which the phase shift is 180 °. This means that the output buffer is intrinsically stable and not prone to oscilla- tion. Most remarkably, the above feature has been achieved in spite of the very low closed loop gain of the amplifier. In contrast, with the classical PNP-NPN stage, the solution adopted for reducing the gain at high frequencies makes use of external RC networks, namely the Boucherot cells. BUILT–IN SHORT CIRCUIT PROTECTION Reliable and safe operation, in presence of all kinds of short circuit involving the outputs is as- sured by BUILT-IN protectors. Additionally to the AC/DC short circuit to GND, to VS, across the speaker, a SOFT SHORT condition is signalled out during the TURN-ON PHASE so assuring cor- Figure 20: The New Output Stage TDA7375A 9/14 |
同様の部品番号 - TDA7375AH |
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同様の説明 - TDA7375AH |
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