Philips TDA8950 User Manual download pdf (Page 6)

Preliminary data sheet Rev. 01 — 9 September 2008 6 of 39

NXP Semiconductors

TDA8950

2 × 150 W class-D power ampliﬁer

The TDA8950 one-chip class-D ampliﬁer contains high power switches, drivers, timing

and handshaking between the power switches and some control logic. Also an advanced

protection strategy is implemented which contains several voltage protections,

temperature protections and a maximum current protection to secure maximum system

robustness.

The two audio channels of the TDA8950 each contain a PWM modulator, an analog

feedback loop and a differential input stage. It also contains circuits common to both

channels such as the oscillator, all reference sources, the mode interface and a digital

timing manager.

The TDA8950 contains two independent ampliﬁer channels with high output power, high

efﬁciency, low distortion and low quiescent current. The ampliﬁer channels can be

connected in the following conﬁgurations:

• Mono Bridge-Tied Load (BTL) ampliﬁer

• Stereo Single-Ended (SE) ampliﬁers

The ampliﬁer system can be switched to one of three operating modes by pin MODE:

• Standby mode; with a very low supply current

• Mute mode; the ampliﬁers are operational, but the audio signal at the output is

suppressed by disabling the VI-converter input stages

• Operating mode; the ampliﬁers are fully operational

To ensure pop noise-free start-up, the DC output offset voltage is applied gradually to the

output at a level between Mute mode and Operating mode levels. The bias current setting

of the VI converters is related to the voltage on pin MODE; in Mute mode the bias current

setting of the VI converters is zero (VI converters disabled) and in Operating mode the

bias current is at maximum. The time constant required to apply the DC output offset

voltage gradually between Mute and Operating mode levels can be generated via an

RC-network on pin MODE. An example of a switching circuit for driving pin MODE is

illustrated in Figure 4. If the capacitor C is left out of the application, the voltage on pin

MODE will be applied with a much smaller time-constant, which might result in audible

pop noises during start-up (depending on DC output offset voltage and loudspeaker

used).

Fig 4. Example of mode selection circuit

001aab172

SGND

MODE pin

mute/on

5 V

standby/

mute

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Philips TDA8950 User Manual Page 6