Philips TDA8571J

2002 Mar 05 5

Philips Semiconductors Product speciﬁcation

4×40 W BTL quad car radio power

ampliﬁer TDA8571J

FUNCTIONAL DESCRIPTION

TheTDA8571J contains four identical amplifiers which can

beused for bridge applications. The gain of each amplifier

is fixed at 34 dB.

Mode select switch (pinMODE)

•Standby: low supply current (<100 µA)

•Mute: input signal suppressed

•Operating: normal on condition.

Sincethis pin has a low input current (<80 µA), a low cost

supply switch can be applied.

Toavoid switch-on plops, it is advised to keep the amplifier

in the mute mode during ≥150ms (charging of the input

capacitors at pins IN1, IN2, IN3 andIN4. When switching

fromstandby to mute, the slope should be at least 18 V/s.

This can be realized by:

•Microprocessor control

•External timing circuit (see Fig.3).

Diagnostic output (pin VDIAG)

DYNAMIC DISTORTIONDETECTOR (DDD)

At the onset of clipping of one or more output stages, the

dynamicdistortion detector becomes active and pin VDIAG

goesLOW. This information can be used to drive a sound

processor or DC volume control to attenuate the input

signal and so limit the distortion. The output level of

pin VDIAG is independent of the number of channels that

are clipping (see Fig.4).

SHORT-CIRCUITDIAGNOSTIC

When a short-circuit occurs at one or more outputs to

ground or to the supply voltage, the output stages are

switched off until the short-circuit is removed and the

deviceis switched on again, with a delay of approximately

10 ms after removal of the short-circuit. During this

short-circuit condition, pin VDIAG is continuously LOW.

Whena short-circuit occurs across the load of one or more

channels, the output stages are switched off during

approximately 10 ms. After that time it is checked during

approximately50 µsto determine whetherthe short-circuit

is still present. Due to this duty cycle of 50 µs/10ms the

average current consumption during this short-circuit

condition is very low.

During this short-circuit condition, pin VDIAG is LOW for

10 ms and HIGH for 50µs (see Fig.5). The protection

circuits of all channels are coupled. This means that if a

short-circuit condition occurs in one of the channels,all

channels are switched off. Consequently, the power

dissipation in any short-circuit condition is very low.

TEMPERATUREPRE-WARNING

Whenthe virtual junction temperature Tvj reaches 145 °C,

pin VDIAG goes LOW.

OPEN-COLLECTOROUTPUTS

The diagnostic pin has an open-collector output, so more

devicescan be tied together. An external pull-up resistor is

needed.

Fig.3 Mode select switch circuitry.

handbook, halfpage

+VP

MODE

MGD959

BZX79C/3.9V

10 kΩ

47 µF

Fig.4 Distortion detector waveform.

handbook, halfpage

MGG155