TAS54x4C Hardware Design Guidelines
1.6
Protection
1.6.1
Voltage Protection
In an automotive environment the typical power supply voltage, PVDD, is the car battery. The battery
voltage can have large voltage swings during the normal operation of the vehicle. The possibility of
unusual events such as load dump are also present. The TAS54x4C devices have protection against over
voltage on the PVDD pin up to 50 V. Undervoltage protections exists on the PVDD, AVDD, DVDD, and
CP pins. The CP and AVDD undervoltage protections are related. If a CP under voltage occurs, the AVDD
voltage is turned off for safety and an AVDD under voltage occurs. In this case, both CP and AVDD
undervoltage bits will be set and the real undervoltage fault is CP.
1.6.2
Over Temperature
The over temperature protection has two modes. One mode is a warning that the device temperature is
high, and the other mode is a shutdown to protect the device from a thermal failure.
NOTE:
The TAS5414C and TAS5424C must have the OTW enabled with I
2
C in register 0x0A, so
that the CLIP_OTW pin will report an overtemperature warning.
The warning mode has three levels. The first warning level triggers the CLIP_OTW pin on the TAS54x4C
and sets a bit in the I
2
C registers. This first warning level triggers at 125°C with a ±13°C. The second level
triggers at 135°C, the third level triggers at 145°C. The temperatures of the levels track to 10°C of each
other with a ±2°C tolerance. For example, if the first level triggers at 115°C, which is inside the tolerance,
then the second level will trigger at 125°C with a tolerance of ±2°C and the third level will trigger at 135°C
with a tolerance of ±2°C.
If the temperature reaches over temperature shutdown near 155°C the device will place the outputs in hi-Z
mode. The I
2
C continues to operate. The tolerance of the temperature is the same as in the above
example.
The overtemperature warning can be used to adjust the volume level or reduce bass in the system, so
that the amplifier will not produce more heat. This warning can also be used to turn on a system fan.
1.6.3
DC Offset
In a car environment with extreme temperature and humidity changes, electronic components such as
electrolytic capacitors can become leaky over time. If this capacitor is used in series with the input signal
and it becomes leaky and DC offset at the speaker outputs could occur. Many other factors cause DC
offset to occur in an audio system.
The DC offset protection monitors the DC output of the amplifier by measuring the width of the pulses over
time. The patented circuitry continuously measures the output, even when a signal is present. The audio
signal does not affect the DC offset measurement. DC offset is necessary in the car environment to
protect against an over-heated voice coil in a speaker. By default the DC offset protection activates the
FAULT pin and places the channel in hi-Z. A bit can be disabled with I
2
C to allow for the channel to remain
in play, but indicate a fault on the FAULT pin and in the fault registers.
1.6.4
Over Current
The TAS54x4C devices provide two types of overcurrent protection. The first is current limiting. The
current-limit method is a straight-line current-limit that is independent of the power supply voltage. Current
limiting is necessary if the output current into the load exceeds a safe level for the device. Instead of
shutting the channel off, the output is limited to the maximum current. The signal to the speaker appears
to be voltage clipped. If the output current-limit is detected continuously for 100 ms then the channel is
placed in hi-Z mode.
The second method in overcurrent protection is a shutdown which places the faulty channel in hi-Z, but
does not turn off the I
2
C. This second method occurs if either amplifier output, post LC filter, is shorted to
the PVDD pin or ground. This protection is not ensured if the IC output pin is shorted to the PVDD pin or
ground.
12
TAS54x4C Design Guide
SLOA196 – June 2014
Copyright © 2014, Texas Instruments Incorporated
