TDA8933B Datasheet, PDF (27/42 Pages) NXP Semiconductors – Class D audio amplifier

NXP Semiconductors
TDA8933B
Class D audio amplifier
14.7 Thermal behavior (PCB considerations)
The TDA8933B is available in a thermally enhanced HTSSOP32 (SOT549-1) package for
reflow soldering.
The HTSSOP32 package has an exposed die pad that reduces significantly the overall
Rth(j-a). Therefore it is required to solder the exposed die pad (at VSSD level) to a copper
plane for cooling. A low thermal-resistance can be achieved when using a multilayer PCB
with sufficient space for two or three thermal planes. Increasing the area of the thermal
plane, the number of planes or the copper thickness can reduce further the thermal
resistance R_th(j-a) of both packages.
Find below the typical thermal resistance (free air and natural convection) of two practical
PCB implementations:
• R_th(j-a) = 48 K/W for a small two-layer application board (55 mm × 40 mm, µm copper,
FR4 base material).
• R_th(j-a) = 30 K/W for a three-layer application board (70 mm × 50 mm, 35 µm copper,
FR4 base material).
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, which is determined by the efficiency of the TDA8933B
The power dissipation is shown in Figure 19 (SE) and Figure 27 (BTL).
Thermal foldback will limit the maximum junction temperature to 140 °C.
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 output capacitors 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
TDA8933B_1
Preliminary data sheet
Rev. 01 — 23 October 2008
© NXP B.V. 2008. All rights reserved.
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