Output Current Limiting - Philips TDA8920B Product Data Sheet

Philips Semiconductors

13.6 Output current limiting

TDA8920B_2
Product data sheet
P
(1) R = 5 K/W.
th(j-a)
(2) R = 10 K/W.
th(j-a)
(3) R = 15 K/W.
th(j-a)
(4) R = 20 K/W.
th(j-a)
(5) R = 35 K/W.
th(j-a)
Fig 8. Derating curves for power dissipation as a function of maximum ambient
temperature
To guarantee the robustness of the class-D amplifier 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 flowing through any of the power switches exceeds the defined 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 amplifier will be regulated to 8 A.
The TDA8920B amplifier can distinguish between a low-ohmic short circuit condition and
other overcurrent conditions like dynamic impedance drops of the loudspeakers used. The
impedance threshold (Z
Depending on the impedance of the short circuit the amplifier will react as follows:
1. Short-circuit impedance > Z
the maximum output current of the amplifier is regulated to 8 A, but the amplifier 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 < Z
the amplifier 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 amplifier will shut-down completely and
an internal timer will be started.
Rev. 02 — 07 November 2005
30
diss
(W)
(1)
20
(2)
10
(3)
(4)
(5)
0
0 20 40
) depends on the supply voltage used.
th
:
th
:
th
TDA8920B
2 × 100 W class-D power amplifier
mbl469
60 80 100
T (°C)
amb
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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