TDA8950 datasheet(21/39 Pages) NXP

21 / 39 page

TDA8950_1

Preliminary data sheet

Rev. 01 — 9 September 2008

21 of 39

NXP Semiconductors

TDA8950

× 150 W class-D power ampliﬁer

100 ms. The average dissipation will be low in this situation because of this low duty cycle.

If the over current condition is removed the ampliﬁer will remain in Operating mode after

being restarted. In this way the TDA8950 ampliﬁer is fully protected against short-circuit

conditions while at the same time so-called audio holes, as a result of loudspeaker

impedance drops, are eliminated.

13.8 Pumping effects

In a typical stereo half-bridge SE application the TDA8950 is supplied by a symmetrical

voltage (e.g. VDD = +35 V and VSS = −35 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. 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 will increase 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 decoupling capacitors on supply lines

• Source and sink currents of other channels

When applying the TDA8950, measures must be taken within the application to minimize

the pumping effect and prevent malfunctions of either the audio ampliﬁer and/or the

voltage supply source. Ampliﬁer malfunction due to the pumping effect can cause

triggering of the UVP, OVP or UBP.

The best remedy against pumping effects is to use the TDA8950 in a mono full-bridge

application or, in the case of stereo half-bridge applications, adapt the power supply (e.g.

increase supply decoupling capacitors).

13.9 Application schematics

Notes for the application schematic:

• A solid ground plane connected to VSS around the switching ampliﬁer is necessary to

prevent emission.

• 100 nF capacitors must be placed as close as possible to the power supply pins of the

TDA8950.

• The internal heat spreader of the TDA8950 is internally connected to VSS.

• The external heatsink must be connected to the ground plane.

• Use a thermally conductive, electrically non-conductive, Sil-Pad between the backside

of the TDA8950 and a small external heatsink.

• The differential inputs enable the best 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. Jumpers J1 and J2 are open on

set level and are closed on the stand-alone demo board.

• Minimum total required capacitance per power supply line is 3300

µF.

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