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TDA8920B Datasheet, PDF (18/34 Pages) NXP Semiconductors – 2 X 100 W class-D power amplifier | |||
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Philips Semiconductors
TDA8920B
2 à 100 W class-D power ampliï¬er
30
Pdiss
(W)
(1)
20
mbl469
(2)
10
(3)
(4)
(5)
0
0
20
40
60
80
100
Tamb (°C)
(1) Rth(j-a) = 5 K/W.
(2) Rth(j-a) = 10 K/W.
(3) Rth(j-a) = 15 K/W.
(4) Rth(j-a) = 20 K/W.
(5) Rth(j-a) = 35 K/W.
Fig 8. Derating curves for power dissipation as a function of maximum ambient
temperature.
13.6 Output current limiting
To guarantee the robustness of the class-D ampliï¬er the maximum output current which
can be delivered by the output stage is limited. An advanced OverCurrent Protection
(OCP) is included for each output power switch.
When the current ï¬owing through any of the power switches exceeds the deï¬ned internal
threshold of 8 A (e.g. in case of a short-circuit to the supply lines or a short-circuit across
the load) the maximum output current of the ampliï¬er will be regulated to 8 A.
The TDA8920B ampliï¬er can distinguish between a low-ohmic short circuit condition and
other overcurrent conditions like dynamic impedance drops of the used loudspeakers. The
impedance threshold (Zth) depends on the supply voltage used.
Depending on the impedance of the short circuit the ampliï¬er will react as follows:
1. Short-circuit impedance > Zth:
the maximum output current of the ampliï¬er is regulated to 8 A, but the ampliï¬er will
not shut-down its PWM outputs. Effectively this results in a clipping output signal
across the load (behavior is very similar to voltage clipping).
2. Short-circuit impedance < Zth:
the ampliï¬er will limit the maximum output current to 8 A and at the same time the
capacitor on the PROT pin is discharged. When the voltage across this capacitor
drops below an internal threshold voltage the ampliï¬er will shut-down completely and
an internal timer will be started.
9397 750 13356
Preliminary data sheet
Rev. 01 â 1 October 2004
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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