TDA8933 Datasheet, PDF (29/47 Pages) NXP Semiconductors – Class-D audio amplifier

NXP Semiconductors
TDA8933
Class-D audio amplifier
14.7 Thermal behavior (printed-circuit board considerations)
The heat sink in an application with a TDA8933 is made using the copper on the
printed-circuit board. The TDA8933 uses the four corner leads (pins 1, 16, 17 and 32) for
heat transfer from the die to the PCB. The thermal foldback will limit the maximum junction
temperature to 140 °C.
Equation 10 shows the relation between the maximum allowable power dissipation P and
the thermal resistance from junction to ambient.
R_{th( j – a)} = ^T-----^j--⁽--^m---^a---^x--_P⁾---^–-----^T----^a--^m----^b
(10)
Where:
R_th(j-a) = thermal resistance from junction to ambient (K/W)
T_j(max) = maximum junction temperature (°C)
T_amb = ambient temperature (°C)
P = power dissipation (W), which is determined by the efficiency of the TDA8933
The power dissipation is shown in Figure 21 (SE) and Figure 33 (BTL).
The thermal resistance, R_th(j-a), of a 2 layer application board (55 mm × 45 mm), 35 µm
copper, FR4 base material in free air with natural convection, is 44 K/W (typ.).
14.8 Pumping effects
When the amplifier is used in an SE configuration, a so-called ‘pumping effect’ can occur.
During one switching interval, energy is taken from one supply (e.g. V_DDP1), while a part of
that energy is delivered back to the other supply line (e.g. V_SSP1), and vice versa. When
the power supply cannot sink energy, the voltage across the output capacitors of that
power supply will increase.
The voltage increase caused by the pumping effect depends on:
• Speaker impedance
• Supply voltage
• Audio signal frequency
• Value of decoupling capacitors on supply lines
• Source and sink currents of other channels
The pumping effect should not cause a malfunction of either the audio amplifier or the
power supply. For instance, this malfunction can be caused by triggering of the
undervoltage or overvoltage protection of the amplifier.
Pumping effects in an SE configuration can be minimized by connecting audio inputs in
anti-phase and changing the polarity of one speaker, as shown in Figure 11.
TDA8933_1
Preliminary data sheet
Rev. 01 — 15 May 2007
© NXP B.V. 2007. All rights reserved.
29 of 47