TDA8920BJ PHILIPS [NXP Semiconductors], TDA8920BJ Datasheet - Page 10

• Manufacturer Part Number: TDA8920BJ
• Description: 2 X 100 W class-D power amplifier
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 13356
Preliminary data sheet
8.3.3 Window Protection (WP)
8.3.4 Supply voltage protections
During the start-up sequence, when pin MODE is switched from standby to mute, the
conditions at the output terminals of the power stage are checked. In the event of a
short-circuit at one of the output terminals to V
interrupted and the system waits for open-circuit outputs. Because the test is done before
enabling the power stages, no large currents will flow in the event of a short-circuit. This
system is called Window Protection (WP) and protects for short-circuits at both sides of
the output filter to both supply lines. When there is a short-circuit from the power PWM
output of the power stage to one of the supply lines (before the demodulation filter) it will
also be detected by the start-up safety test. Practical use of this test feature can be found
in detection of short-circuits on the printed-circuit board.
Remark: This test is operational during (every) start-up sequence at a transition between
Standby and Mute mode. However when the amplifier is completely shut-down due to
activation of the OverCurrent Protection (OCP) because a short to one of the supply lines
is made, then during restart (after 100 ms) the window protection will be activated. As a
result the amplifier will not start-up until the short to the supply lines is removed.
If the supply voltage drops below 12.5 V, the UnderVoltage Protection (UVP) circuit is
activated and the system will shut-down 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
shut-down. It is re-enabled as soon as the supply voltage drops below the threshold level.
So in this case no timer of 100 ms is started.
An additional UnBalance Protection (UBP) circuit compares the positive analog (V
and the negative analog (V
between them exceeds a certain level. This level depends on the sum of both supply
voltages. An expression for the unbalanced threshold level is as follows:
V
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 9 V; see also
In
Table 4:
[1]
Protection name
OTP
OCP
WP
UVP
OVP
UBP
33 V the OverVoltage Protection (OVP) circuit is activated and the power stages will
th(ub)
Table 4
Hysteresis of 20 degrees will influence restart timing depending on heatsink size.
0.15
an overview is given of all protections and the effect on the output signal.
Overview protections TDA8920B
(V
DDA
+ V
Rev. 01 — 1 October 2004
Complete shut-down
Y
N
Y
Y
Y
Y
[3]
[2]
SSA
SSA
).
) supply voltages and is triggered if the voltage difference
Restart directly
Y
Y
Y
N
Y
N
DD
[1]
[2]
Section
or V
2
SS
13.7.
the start-up procedure is
100 W class-D power amplifier
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
TDA8920B
Restart every 100 ms
N
N
N
Y
N
Y
[1]
[2]
DDA
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)