TDA8954_1 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 01 — 24 December 2009 26 of 46
NXP Semiconductors
TDA8954
2 × 210 W class-D power amplifier
R
th(h-a)
(thermal resistance from heatsink to ambient) = 10.3 − (0.9 + 1) = 8.4 K/W
The derating curves for power dissipation (for several R
th(j-a)
values) are illustrated in
Figure 12. A maximum junction temperature T
j
= 150 °C is taken into account. The
maximum allowable power dissipation for a given heatsink size can be derived, or the
required heatsink size can be determined, at a required power dissipation level; see
Figure 12.
14.6 Pumping effects
In a typical stereo single-ended configuration, the TDA8954 is supplied by a symmetrical
supply voltage (e.g. V
DD
= +41 V and V
SS
= −41 V). When the amplifier is used in an SE
configuration, a ‘pumping effect’ can occur. During one switching interval, energy is taken
from one supply (e.g. V
DD
), while a part of that energy is returned to the other supply line
(e.g. V
SS
) and vice versa. When the voltage supply source cannot sink energy, the voltage
across the output capacitors of that voltage supply source increases and the supply
voltage is pumped to higher levels. The voltage increase caused by the pumping effect
depends on:
• Speaker impedance
• Supply voltage
• Audio signal frequency
• Value of supply line decoupling capacitors
• Source and sink currents of other channels
Pumping effects should be minimized to prevent the malfunctioning of the audio amplifier
and/or the voltage supply source. Amplifier malfunction due to the pumping effect can
trigger UVP, OVP or UBP.
The most effective way to avoid pumping effects is to connect the TDA8954 in a mono
full-bridge configuration. In the case of stereo single-ended applications, it is advised to
connect the inputs in anti-phase (see
Section 8.5 on page 14). The power supply can also
be adapted; for example, by increasing the values of the supply line decoupling
capacitors.
14.7 Application schematic
Notes on the application schematic:
• Connect a solid ground plane around the switching amplifier to avoid emissions
• Place 100 nF capacitors as close as possible to the TDA8954 power supply pins
• Connect the heatsink to the ground plane or to VSSPn using a 100 nF capacitor
• Use a thermally conductive, electrically non-conductive, Sil-Pad between the
TDA8954 heat spreader and the external heatsink
• The heat spreader of the TDA8954 is internally connected to VSSA
• Use differential inputs for the most effective system level audio performance with
unbalanced signal sources. In case of hum due to floating inputs, connect the
shielding or source ground to the amplifier ground.
