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TDA7256 Folha de dados(PDF) 7 Page - STMicroelectronics |
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TDA7256 Folha de dados(HTML) 7 Page - STMicroelectronics |
7 / 10 page CIRCUIT DESCRIPTION INPUT STAGE The input stage is a differential type preamplifier stage with two independent inputs and two out- puts in phase opposition. It is designed for particular linearity characteristics in order to have output amplitude large enough (1VPP) yet maintaining low distortion. The voltage gain of the stage is 6 dB.The possi- bility to use the differential input allows the sys- tem immunity to common-mode noise in case of long wire connections (fig. 17 ) MUTE The mute circuit (TTL compatible) acts at pream- plifier level and disables the inputs without chang- ing the DC voltage values. In such a way the op- eration is fully popless.The use of a RC network produces a soft reduction of the audio signal pro- viding the best effect from the acoustic point of view (fig 18). The mute circuit is also activated during turn- on/turn-off operations when the voltage at stand- by pin is lower than about 2 volt TURN-ON The TDA7256 is fully popless at turn-on thanks to a delay circuit which keeps the output low during the capacitors charge transient. The delay-time is given by the following formula: TURN-OFF The ground compatible structures and the choice of a soft turn-off circuit ensure a fully popless op- eration. OUTPUT STAGE It is a power stage designed in a way of being able to drive loads up to 2 ohm in bridge configu- ration without bootstrap capacitors (22 W with RL=4 ohm , 30W with RL=2 ohm). SVR The noises coming from the car environment are essentially inside the bandwith from 300 Hz to 6 KHz. The ripple rejection circuit which utilizes also the gain capacitors C11,C9 ensures in this frequency range a rejection typ. of 60dB. SHORT CIRCUIT PROTECTION The short circuit protection circuits intervene in the following cases: - s.c. between one output and ground - s.c. between one output and +Vs - s.c. between the outputs In the first two cases they stop the current in both the final stages,allowing also loudspeaker protec- tion.In the last case the current is limited, thus avoiding the load point to reach the SOA of the output transistors. STAND-BY In stand-by condition the current generators are disabled:the current drops to a very low value (few µA). Also this function is fully popless. Fig. 19 shows the silent transients of turn-on and turn-off operations through both the mute and the stand-by pins. Figure 18: Soft Muting To = 800 C10 + 600 (C9 + C11) ( C10 C9 + C11 + 1 ) Figure 17: Balanced -Unbalanced Input TDA7256 7/10 |
Nº de peça semelhante - TDA7256 |
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Descrição semelhante - TDA7256 |
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