TDA8948J_1
© NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 01 — 27 February 2008
6 of 26
NXP Semiconductors
TDA8948J
4-channel audio amplifier
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 7
.
The maximum output power is limited by the supply voltage (V
CC
= 26 V) and the
maximum output current (I
O
= 4 A repetitive peak current).
For supply voltages V
CC
> 22 V, a minimum load is required; see
Figure 5
:
•
SE: R
L
= 3
Ω
•
BTL: R
L
= 6
Ω
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.
The Average Listening Level (ALL) music power, without any distortion, yields:
•
SE at P
o(SE)
= 5 W, V
CC
= 17 V, R
L
= 4
Ω
and THD = 0.2 %:
(4)
•
BTL at P
o(BTL)
= 10 W, V
CC
= 17 V, R
L
= 8
Ω
and THD = 0.1 %:
(5)
The power dissipation can be derived from
Figure 8
(SE and BTL) for a headroom of 0 dB
and 12 dB, respectively.
For heat sink calculation at the average listening level, a power dissipation of 9 W can be
used.
8.3 Mode selection
The TDA8948J has three functional modes which can be selected by applying the proper
DC voltage to pin MODE1.
Standby - The current consumption is very low and the outputs are floating. The device is
in standby mode when V
MODE1
< 0.8 V, or when the MODE1 pin is grounded. In standby
mode, the function of pin MODE2 has been disabled.
Mute - The amplifier is DC-biased, but not operational (no audio output). This allows the
input coupling capacitors to be charged to avoid pop-noise. The device is in mute mode
when 4.5 V < V
MODE1
< (V
CC
- 3.5 V).
Table 4.
Power rating as function of headroom
Headroom
Power output
Power dissipation
(all channels driven)
SE
BTL
0 dB
P
o
= 5 W
P
o
= 10 W
P = 17 W
12 dB
P
o(ALL)
= 315 mW
P
o(ALL)
= 630 mW
P = 9 W
P
o ALL
(
)
SE
5 10
3
⋅
15.85
---------------
315 mW
=
=
P
o ALL
(
)
BTL
10 10
3
⋅
15.85
------------------
630 mW
=
=
