February 1995

5

Philips Semiconductors

Preliminary specification

2

× 24 W BTL or 4 × 12 W single-ended car

radio power amplifier

TDA8564Q

Diagnostic output (pin 16)

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

dynamic distortion detector becomes active and pin 16

goes LOW. This information can be used to drive a sound

processor or DC volume control to attenuate the input

signal and thus limit the distortion. The output level of

pin 16 is independent of the number of channels that are

clipping (see Figs 4 and 5).

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

device is switched on again, with a delay of approximately

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

short-circuit condition, pin 16 is continuously LOW.

When a short-circuit across the load of one or more

channels occurs the output stages are switched off during

approximately 20 ms. After that time it is checked during

approximately 50

µs to see whether the short-circuit is still

present. Due to this duty cycle of 50

µs/20 ms the average

current consumption during this short-circuit condition is

very low (approximately 40 mA).

During this short-circuit condition, pin 16 is LOW for 20 ms

and HIGH for 50

µs (see Fig.6).

The power dissipation in any short-circuit condition is

very low.

pin 16 will be active LOW.

Pin 16 is an open-collector output, which allows pin 16 of

more devices being tied together.

Fig.4 Distortion detector waveform; BTL application.

handbook, halfpage

V

0

VP

VO

0

t

MGA705

16

Fig.5

Distortion detector waveform; single-ended

application.

handbook, halfpage

0

VP

VO

t

0

MGA706

V16

Fig.6 Short-circuit waveform.

handbook, full pagewidth

MGA707

short-circuit over the load

20 ms

50

µs

t

t

VP

current

in

output

stage

V16