TDA8922C NXP Semiconductors, TDA8922C Datasheet - Page 20

• Manufacturer Part Number: TDA8922C
• Description: The TDA8922C is a high-efficiency Class D audio power amplifier
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TDA8922C_1
Product data sheet
13.6 Pumping effects
In the following example, a heatsink calculation is made for an 8
When the maximum expected ambient temperature is 50 C, the total R
R
So the thermal resistance between heatsink and ambient temperature is:
The derating curves for power dissipation (for several R
Figure
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
In a typical stereo single-ended configuration, the TDA8922C is supplied by a symmetrical
supply voltage (e.g. V
configuration, a ‘pumping effect’ can occur. During one switching interval, energy is taken
from one supply (e.g. V
(e.g. V
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:
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.
-------------------------
30 V supply:
150 50
•
•
•
•
•
th(j-a)
The audio signal has a crest factor of 10 (the ratio between peak power and average
power (20 dB)); this means that the average output power is
Thus, the peak RMS output power level is the 0.5 % THD level, i.e. 110 W.
The average power is then
The dissipated power at an output power of 11 W is approximately 5 W.
R
R
mounting)
R
th(j-c)
th(c-h)
th(h-a)
Speaker impedance
Supply voltage
Audio signal frequency
Value of supply line decoupling capacitors
Source and sink currents of other channels
5
–
SS
= R
9. A maximum junction temperature T
9.
(thermal resistance from junction to case) = 1.5 K/W
) and vice versa. When the voltage supply source cannot sink energy, the voltage
(thermal resistance from case to heatsink) = 0.5 K/W to 1 K/W (dependent on
(thermal resistance from heatsink to ambient) = 20
th(j-c)
=
20 K/W
+ R
th(c-h)
Rev. 01 — 7 September 2009
DD
DD
+ R
= 30 V and V
), while a part of that energy is returned to the other supply line
th(h-a)
1
10
110 W = 11 W.
SS
= 30 V). When the amplifier is used in an SE
j
= 150 C is taken into account. The
2
th(j-a)
75 W class-D power amplifier
values) are illustrated in
(1.5 + 1) = 17.5 K/W
1
10
of the peak power.
BTL application with a
TDA8922C
© NXP B.V. 2009. All rights reserved.
th(j-a)
becomes
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