TDA8922CJ View Datasheet(PDF) - NXP Semiconductors.
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TDA8922CJ Datasheet PDF : 40 Pages
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NXP Semiconductors
TDA8922C
2 × 75 W class-D power ampliï¬er
In the following example, a heatsink calculation is made for an 8 Ω BTL application with a
±30 V supply:
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 1â„10 of the peak power.
Thus, the peak RMS output power level is the 0.5 % THD level, i.e. 110 W.
The average power is then 1â„10 × 110 W = 11 W.
The dissipated power at an output power of 11 W is approximately 5 W.
When the maximum expected ambient temperature is 50 °C, the total Rth(j-a) becomes
(---1---5---0---5-–-----5---0----) = 20 K/W
Rth(j-a) = Rth(j-c) + Rth(c-h) + Rth(h-a)
Rth(j-c) (thermal resistance from junction to case) = 1.5 K/W
Rth(c-h) (thermal resistance from case to heatsink) = 0.5 K/W to 1 K/W (dependent on
mounting)
So the thermal resistance between heatsink and ambient temperature is:
Rth(h-a) (thermal resistance from heatsink to ambient) = 20 − (1.5 + 1) = 17.5 K/W
The derating curves for power dissipation (for several Rth(j-a) values) are illustrated in
Figure 9. A maximum junction temperature Tj = 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 9.
13.6 Pumping effects
In a typical stereo single-ended conï¬guration, the TDA8922C is supplied by a symmetrical
supply voltage (e.g. VDD = 30 V and VSS = −30 V). When the ampliï¬er is used in an SE
conï¬guration, a ‘pumping effect’ can occur. During one switching interval, energy is taken
from one supply (e.g. VDD), while a part of that energy is returned to the other supply line
(e.g. VSS) 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 ampliï¬er
and/or the voltage supply source. Ampliï¬er malfunction due to the pumping effect can
trigger UVP, OVP or UBP.
TDA8922C_1
Product data sheet
Rev. 01 — 7 September 2009
© NXP B.V. 2009. All rights reserved.
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