Philips Semiconductors
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TDA1562Q application note
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© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Application note
Rev. 01.02 — 05 May 2006
17 of 62
The TDA 1562Q has two separate circuits, protecting it against short circuits to the
ground, the supply voltage and across the load.
The first protection circuit, the
missing current protection
will switch off the amplifier in
case of a short circuit to ground or to the supply. The missing current protection
compares the current flowing into the supply pins with the current flowing out of the
power ground pins. As soon as the difference between the two measured values
exceeds 1.5A the amplifier is switched off. Such a situation will occur as soon as one of
the outputs is shorted to either ground or to the supply.
The second short circuit protection is called the
maximum current protection
. This
protection is activated as soon as the current in the output stage exceeds 7.5A.
This will happen when there is a short between the two outputs. For this protection to be
activated, it is necessary that there is a signal at the output of the amplifier, otherwise no
current will be flowing between the outputs.
When a too low impedance is connected to the amplifier (2
Ω
) this protection can also be
activated when the amplifier is driven hard and cause “audio holes”.
In the situations described above, the amplifier will be protected against damage by the
protection circuits.
There are, however, some conditions which will damage the device. Generally, double
fault conditions and fault conditions under more extreme circumstances may damage the
device.
Examples of double faults are:
-Short circuit of one of the outputs to ground while the power ground is disconnected.
(also known as loss of ground condition)
-Short circuit of one of the outputs to the supply while the supply is disconnected.
During operation at supply voltages higher than 16V, the charge circuits for the lifter
capacitors and the voltage lifting circuits will heat up considerably, especially when the
amplifier is driven by a signal with a large low frequency content.
In extreme conditions (continuous clipping signal), the charging and/or lifting circuits may
overheat after prolonged operation.
A number of other conditions that are known to have caused damage to the TDA1562Q
are:
1. Driving the amplifier into thermal protection while the device is forced into class H
mode by means of the status I/O pin. Normally, when the status I/O pin is floating,
the thermal protection will disable class H operation when a heatsink temperature of
120
o
C is reached (approximately 145
o
C junction temperature). When this protection
is overruled by connecting the status I/O pin to the supply, there is a serious risk of
overheating the lifting circuitry.
Driving the device so hard that the overall thermal shutdown is activated will in this
situation cause overheating of the lifting circuitry, possibly resulting in permanent
damage to the lifting circuits.
2. Shorting an output to the Vsupply while the corresponding lifter capacitor is fully
discharged.
This situation can occur when a device is switched on instantaneously after the
power supply is connected, with an input signal so high, that the amplifier is forced
into Class H mode immediately. This can only occur when the mode select pin is
high at the moment that the supply is connected to the amplifier. Normally when
