Philips TDA8944J - Manual (Page 5)

NXP Semiconductors
TDA8944J
2 x 7 W stereo BTL audio amplifier
Product specification Rev. 02 — 14 February 2000 5 of 22
9397 750 06861 © NXP B.V. 2010. All rights reserved.
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 V
CC
= 12 V, R
L
= 8
Ω and P
o
= 4 W at THD = 0.1% (see Figure 6 ), the
Average Listening Level (ALL) – music power – without any distortion yields:
P
o(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.
8.3 Mode selection
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 (V
CC
− 0.5 V) < V
MODE
< 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 P
o
= 4 W 8 W
12 dB P
o(ALL)
= 252 mW 4 W