Philips TDA1562Q - 8 Driving a Dual Voice Coil Speaker; Pulses below Substrate Level at the Outputs

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 49 of 62
8. Driving a dual voice coil speaker
Driving a dual voice coil subwoofer with two TDA1562 amplifiers may cause a number of
fault conditions which could damage the amplifier.
The next paragraphs will explain which fault conditions may occur and give suggestions
on how the amplifiers can be protected against these fault conditions.
8.1 Pulses below substrate level at the outputs
When one of the two amplifiers is driven so hard that the lift capacitors are fully
discharged, it may occur that the other amplifier will induce voltage pulses into the output
of this amplifier, due to the cross coupling between the two loudspeaker coils.
One possible condition which has been observed is that pulses below substrate level
occur at the output of the amplifier. As soon as the voltage at the output is pulled more
than 0.7V below substrate (ground) level, a parasitic diode in the output stage (see
fig.37) will start conducting. When the current through this parasitic diode exceeds
approx.3.5A, damage to the output stage will occur.
Fig 37. One output stage of the TDA1562 with negative pulse
Parasitic
Clift
Vsupply
Pgnd
SPEAKER
0
Vpulse