TDA8920C datasheet(21/40 Pages) NXP

21 / 40 page

TDA8920C_1

Preliminary data sheet

Rev. 01 — 29 September 2008

21 of 40

NXP Semiconductors

TDA8920C

× 110 W class-D power ampliﬁer

A typical value for the capacitor connected to pin PROT can be from 10 pF to 220 pF; see

Figure 10. After a ﬁxed time of 100 ms the ampliﬁer switches on. If the requested output

current is still too high, the ampliﬁer switches off. Thus the ampliﬁer tries to switch to the

Operating mode every 100 ms. The average power dissipation will be low in this situation

because of the low duty cycle.

If the overcurrent condition is removed, the ampliﬁer stays in Operating mode after

restarting. This fully protects the TDA8920C ampliﬁer against short-circuit conditions while

at the same time eliminating so-called audio holes resulting from loudspeaker impedance

drops.

[1]

Overvoltage protection activation caused by supply pumping due to the weak short-circuit; see

Section 13.8.

13.8 Pumping effects

In a typical stereo half-bridge SE application the TDA8920C is supplied by a symmetrical

voltage (e.g. VDD = 30 V and VSS = −30 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 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

In applications using the TDA8920C ensure pumping effects are minimized and prevent

malfunctions of either the audio ampliﬁer and/or the voltage supply source. Ampliﬁer

malfunction due to the pumping effect can trigger UVP, OVP or UBP.

The most effective solution against pumping effects is to use the TDA8920C in a mono

full-bridge application. In the case of stereo half-bridge applications, adapt the power

supply, for example, by increasing the values of the supply decoupling capacitors.

Table 11.

Current limiting behavior during low output impedance conditions at different

values of CPROT

Type

(V)

VI (mV, p-p) f (Hz) CPROT

(pF)

PWM output stops

Short (0

Ω) Short (0.5 Ω) Short (1 Ω)

TDA8920CJ/N1

29.5 500

yes

OVP[1]

1000

yes

OVP[1]

1000

yes

1000

220

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