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Objective data sheet

Rev. 01 — 22 April 2004

5 of 21

Philips Semiconductors

TDA8939

Zero dead time Class-D 7.5 A power comparator

8.

Functional description

8.1 General

The TDA8939 class-D power comparator is designed for use in fully digital open-loop

class-D audio applications. Excellent timing accuracy with respect to delay times and rise

and fall times is achieved and one of the most important sources of distortion in a full

digital open-loop audio amplifier is eliminated; the zero dead time switching concept is

included. The TDA8939 contains two independent class-D output stages with high power

D-MOS switches, drivers, timing and control logic. For protection a temperature sensor, a

maximum current detection and overvoltage detection circuit are integrated. An internal

protection latch keeps the power comparator in shut-down mode after a fault condition has

been detected. External reset of the latch is required via the enable input.

8.2 Protections

Overtemperature, overcurrent and overvoltage sensors are included in the TDA8939

power comparator. In the event that the maximum temperature, maximum current or

maximum supply voltage is exceeded the diagnostic output is activated (open-drain output

pulled-down via external pull-up resistor).

The diagnostic output pin is activated (active LOW) in case of:

2. Overcurrent (OCP): the output current exceeds the maximum output current threshold

level (e.g. when the loudspeaker terminals are short-circuited it will be detected by the

current protection).

3. Overvoltage (OVP): the supply voltage applied to the power comparator exceeds the

maximum supply voltage threshold level.

The TDA8939 is self-protecting. If a fault condition (OTP, OCP or OVP) is detected it will

pull-down the diagnostic output (pin 7), while at the same time shutting down the power

stage. In case of a fault condition in one of the half-bridges or output channel the other

half-bridge and output channel will also shut down. All protections trigger a latch which

ensures that the power stage remains deactivated until the latch is reset again.

The latch is reset by switching the enable voltage of the power stage to LOW level. Both

set (S) and reset (R) inputs of the protection latch trigger on a negative falling slope.

STAB1

19

decoupling internal stabilizer for logic supply channel 1

20

negative power supply voltage for channel 1

OUT1

21

PWM output channel 1

BOOT1

22

bootstrap capacitor 1

23

positive power supply voltage for channel 1

24

negative digital supply voltage

SUB

-

Table 3:

Symbol

Pin

Description