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ShortDetected
OpenDetected
NormalLoadDetected
ShortDetection
Range
OpenDetection
Range
0.5
300
1.5
1300
1(Typ)
800(Typ)
R
(IncludingWires)
Load
M0067-01
Protection and Monitoring
SLOS514A – FEBRUARY 2007 – REVISED JULY 2007
DESCRIPTION OF OPERATION (continued)
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 TAS5414 and TAS5424) 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 TAS5414 and TAS5424 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
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