Philips Semiconductors

TDA8944J

2 x 7 W stereo BTL audio amplifier

Product specification

Rev. 02 — 14 February 2000

6 of 21

9397 750 06861

© Philips Electronics N.V. 2000. All rights reserved.

Mute — In this mode the amplifier is DC-biased but not operational (no audio output);

allows the input coupling and Supply Voltage Ripple Rejection (SVRR) capacitors to

be charged to avoid pop-noise. The device is in mute mode when

Operating — In this mode the amplifier is operating normally. The operating mode is

8.3.1

Switch-on and switch-off

To avoid audible plops during supply voltage switch-on or switch-off, the device is set

to standby mode before the supply voltage is applied (switch-on) or removed

(switch-off).

The switch-on and switch-off time can be influenced by an RC-circuit on the MODE

pin. Rapid on/off switching of the device or the MODE pin may cause ‘click- and

pop-noise’. This can be prevented by proper timing of the RC-circuit on the MODE

pin.

8.4 Supply Voltage Ripple Rejection (SVRR)

The SVRR is measured with an electrolytic capacitor of 10

µF on pin SVR at a

bandwidth of 10 Hz to 80 kHz. Figure 13 on page 11 illustrates the SVRR as function

of the frequency. A larger capacitor value on the SVR pin improves the ripple rejection

behaviour at the lower frequencies.

8.5 Built-in protection circuits

The TDA8944J contains two types of protection circuits, i.e. short-circuit and thermal

shutdown.

8.5.1

Short-circuit protection

Short-circuit to ground or supply line — This is detected by a so-called ‘missing

current’ detection circuit which measures the current in the positive supply line and

the current in the ground line. A difference between both currents larger than 0.4 A,

switches the power stage to standby mode (high impedance).

Short-circuit across the load — This is detected by an absolute-current

measurement. An absolute-current larger than 2 A, switches the power stage to

standby mode (high impedance).

8.5.2

Thermal shutdown protection

The junction temperature is measured by a temperature sensor; at a junction

temperature of approximately 150

°C this detection circuit switches the power stage

to standby mode (high impedance).