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ShortDetected

OpenDetected

NormalLoadDetected

ShortDetection

Range

OpenDetection

Range

0.5

300

1.5

1300

1(Typ)

800(Typ)

(IncludingWires)

Load

M0067-01

Protection and Monitoring

TAS5414A, TAS5424A

SLOS535A – JULY 2007 – REVISED FEBRUARY 2008

Figure 14. Open and Shorted Load Detection

2. Tweeter Detection—The tweeter detection function is an ac diagnostic used to determine proper connection

of the tweeter when a passive crossover is used. The proper implementation of this diagnostic function is

dependent on the amplitude of a user-supplied test signal and on the impedance vs frequency curve of the

acoustic package. The tweeter function is invoked via I2C, and all four channels should be tested individually.

The tweeter detection uses the average cycle-by-cycle current limit circuit (see CBC section) to measure the

current to the load. The current level for the tweeter detection threshold is typically 550 mA. The system

(external to the TAS5414A and TAS5424A) must generate a tone burst in the 10-kHz to 25-kHz range. If the

tone burst employs a frequency higher than 20 kHz, and if a sufficiently smooth amplitude ramp is used, the

tweeter detection signal is silent. The frequency and amplitude of this tone burst must be calibrated by the

user to result in a current draw greater than the selected threshold level when the tweeter is present. The

tweeter detection results are monitored on the CLIP_OTW pin during the application of the test tone. If the

current threshold is attained during measurement, the tweeter is present; then the CLIP_OTW pin is

asserted. When the tweeter detector is activated, pulses on the CLIP_OTW pin begin to toggle at 250 kHz to

500 kHz. As the detection signal gets stronger due to higher load current, the density (or duty cycle) of the

pulses increases.

1. Cycle-By-Cycle Current Limit (CBC)—The CBC current-limiting circuit terminates each PWM pulse to limit

the output current flow when the average current limit (ILIM) threshold is exceeded. The overall effect on the

audio in the case of a current overload is quite similar to a voltage-clipping event, where power is temporarily

limited at the peaks of the musical signal and normal operation continues without disruption when the

overload is removed. The TAS5414A and TAS5424A do not prematurely shut down in this condition. All four

channels continue in play mode and pass signal.

2. Overcurrent Shutdown (OCSD)—Under severe short-circuit events, such as a short to PVDD or ground, a

peak-current detector is used, and the affected channel shuts down in 200

µs to 390 µs if the conditions are

severe enough. The shutdown speed depends on a number of factors, such as the impedance of the short

circuit, supply voltage, and switching frequency. Only the shorted channels are shut down in such a scenario.

The user may restart the affected channel via I2C. An OCSD event activates the fault pin, and the affected

channel(s) are recorded in the I2C fault register. If the supply or ground short is strong enough to exceed the

peak current threshold but not severe enough to trigger the OCSD, the peak current limiter prevents excess

current from damaging the output FETs, and operation returns to normal after the short is removed.

3. DC Detect—This circuit detects a dc offset continously during normal operation at the output of the amplifier.

If the dc offset reaches the level defined in the I2C registers for the specified time period, the circuit triggers.

By default a dc detection event does not shut the output down. The shutdown function can be enabled or

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