Philips TDA8944J 8.2 Power amplier, , 8.3 Mode selection

Philips Semiconductors TDA8944J

2 x 7 W stereo BTL audio ampliﬁer

Product speciﬁcation Rev. 02 — 14 February 2000 5 of 21

8.2 Power ampliﬁer

The power ampliﬁer is a Bridge Tied Load (BTL) ampliﬁer with an all-NPN output

stage, capable of delivering a peak output current of 2 A.

The BTL principle offers the following advantages:

•Lower peak value of the supply current

•The ripple frequency on the supply voltage is twice the signal frequency

•No expensive DC-blocking capacitor

•Good low frequency performance.

8.2.1 Output power measurement

The output power as a function of the supply voltage is measured on the output pins

at THD = 10%; see Figure 8. The maximum output power is limited by the maximum

supply voltage of 12 V and the maximum available output current: 2 A repetitive peak

current.

8.2.2 Headroom

Typical CD music requires at least 12 dB (factor 15.85) dynamic headroom –

compared to the average power output – for transferring the loudest parts without

distortion. At VCC =12V, R

L=8Ω and Po= 4 W at THD = 0.1% (see Figure 6), the

Average Listening Level (ALL) – music power – without any distortion yields:

Po(ALL) = 4 W/15.85 = 252 mW.

The power dissipation can be derived from Figure 11 on page 10 for 0 dB

respectively 12 dB headroom.

For the average listening level a power dissipation of 4 W can be used for a heatsink

calculation.

The TDA8944J has three functional modes, which can be selected by applying the

proper DC voltage to pin MODE. See Figure 4 and 5 for the respective DC levels,

which depend on the supply voltage level. The MODE pin can be driven by a 3-state

logic output stage: e.g. a microcontroller with additional components for DC-level

shifting.

Standby — In this mode the current consumption is very low and the outputs are

ﬂoating. The device is in standby mode when (VCC −0.5 V) < VMODE <V

CC, or when

the MODE pin is left ﬂoating (high impedance). The power consumption of the

TDA8944J will be reduced to <0.18 mW.

Table 4: Power rating as function of headroom

Headroom Power output (THD = 0.1%) Power dissipation (P)

0 dB Po=4W 8W

12 dB Po(ALL) = 252 mW 4 W