TDA8920C Datasheet, PDF (21/40 Pages) NXP Semiconductors – 2 X110 W class-D power amplifier

NXP Semiconductors
TDA8920C
2 × 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.
Table 11.
Type
Current limiting behavior during low output impedance conditions at different
values of C_PROT
V_P V_I (mV, p-p) f (Hz) C_PROT PWM output stops
(V)
(pF) _{Short (0 Ω) Short (0.5 Ω) Short (1 Ω)}
TDA8920CJ/N1 29.5 500
20 10 yes
yes
OVP^[1]
1000 10 yes
yes
no
20 15 yes
yes
OVP^[1]
1000 15 yes
no
no
1000 220 no
no
no
[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. V_DD = 30 V and V_SS = −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. V_DD), while a part of that energy is returned to the other supply line
(e.g. V_SS) 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.
TDA8920C_1
Preliminary data sheet
Rev. 01 — 29 September 2008
© NXP B.V. 2008. All rights reserved.
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