1-watt BTL audio amplifier

1-watt BTL audio amplifier
The TDA8581(T) from PhilipsSemiconductors is a 1-wattBridge Tied Load (BTL) audiopower amplifier capable of delivering1 watt output power into an8-Ωload at THD (total harmonicdistortion) of 10% and using a 5-V power supply. The schematicshown here combines the functionaldiagram of the TDA8551with its typical application circuit.The gain of the amplifiercan be set by the digital volumecontrol input. At the highest volumesetting, the gain is 20 dB.Using the MODE pin the devicecan be switched to one of threemodes: standby (MODE levelbetween Vp and Vp–0.5 V),muted (MODE level between1 V and Vp–1.4 V) or normal(MODE level less than 0.5 V).The TDA8551 is protected by aninternal thermal shutdown protectionmechanism.The total voltage loss for bothMOS transistors in the complementaryoutput stage is less than1 V. Using a 5-V supply and an8-Ω loudspeaker, an outputpower of 1 watt can be delivered.

The volume control has anattenuation range of between0 dB and 80 dB in 64 steps setby the 3-state level at theUP/DOWN pin: floating: volumeremains unchanged; negativepulses: decrease volume;positive pulses: increase volumeEach pulse at he Up/DOWN pincauses a change in gain of 80/64= 1.25 dB (typical value).When the supply voltage is firstconnected, the attenuator is setto 40 dB (low volume), so thegain of the total amplifier is then–20 dB. Some positive pulseshave to be applied to theUP/DOWN pin to achieve listeningvolume. The graph showsthe THD as a function of outputpower. The maximum quiescentcurrent consumption of theamplifier is specified at 10 mA,to which should be added thecurrent resulting from the outputoffset voltage divided by theload impedance.

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