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TDA8950_1 © NXP B.V. 2008. All rights reserved.
Preliminary data sheet Rev. 01 — 9 September 2008 10 of 39
NXP Semiconductors
TDA8950
2 × 150 W class-D power amplifier
Should there be an impedance drop (e.g. due to dynamic behavior of the loudspeaker) the
same protection will be activated. The maximum output current will again be limited to
9.2 A, but the amplifier will not switch-off completely (thus preventing audio holes from
occurring).
The result will be a clipping output signal.
See Section 13.7 for more information on this maximum output current limiting feature.
8.3.3 Window Protection (WP)
The WP checks the conditions at the output terminals of the power stage and is activated:
• During the start-up sequence, when pin MODE is switched from standby to mute. In
the event of a short-circuit at one of the output terminals to pin VDDPn or pin VSSPn
the start-up procedure is interrupted and the TDA8950 waits until the short-circuit to
the supply lines has been removed. Because the test is done before enabling the
power stages, no large currents will flow in an event of short-circuit.
• When the amplifier is completely shut-down due to activation of the OCP because a
short-circuit to one of the supply lines is made, then during restart (after 100 ms) the
WP will be activated. As a result the amplifier will not start-up until the short-circuit to
the supply lines is removed.
8.3.4 Supply voltage protections
If the supply voltage drops below minimum supply voltage, the UVP circuit is activated and
the system will shutdown correctly. If the internal clock is used, this switch-off will be silent
and without pop noise. When the supply voltage rises above the threshold level, the
system is restarted again after 100 ms.
If the supply voltage exceeds maximum supply voltage, the OVP circuit is activated and
the power stages will shutdown. When the supply voltage drops below the threshold level,
the system is restarted again after 100 ms.
An additional UBP circuit compares the positive analog (voltage on pin VDDA) and the
negative analog (voltage on pin VSSA) supply voltage and is triggered if the voltage
difference exceeds a factor of two.
When the supply voltage difference drops below the threshold level, the system is
restarted again after 100 ms.
Example: With a symmetrical supply of ±30 V, the protection circuit will be triggered if the
unbalance exceeds approximately 15 V. See Section 13.7.
In Table 4 an overview is given of all protections and their respective effects on the output
signal.