TDA8944J datasheet(6/21 Pages) PHILIPS

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Philips Semiconductors

TDA8944J

2 x 7 W stereo BTL audio ampliﬁer

Product speciﬁcation

Rev. 02 — 14 February 2000

6 of 21

9397 750 06861

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

the DC level of the input and output pins remain on half the supply voltage. This

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

3V<VMODE <(VCC − 1.5 V).

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

activated at VMODE < 0.5 V.

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).

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