HS PWM

PWM_X

LS PWM

OC EVENT RESETS

CB3C LATCH

OUTPUT CURRENT

OC THRESHOLD

OCH

HS GATE-DRIVE

LS GATE-DRIVE

RISING EDGE PWM

SETS CB3C LATCH

23

TPA3221

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SLASEE9 – JUNE 2017

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Figure 18. CB3C Timing Example

9.4.5.2 Signal Clipping and Pulse Injector

A built in activity detector monitors the PWM activity of the OUT_X pins. TPA3221 is designed to drive

unclipped output signals all the way to PVDD and GND rails. In case of audio signal clipping when applying

excessive input signal voltage, or in case of CB3C current protection being active, the amplifier feedback

loop of the audio channel will respond to this condition with a saturated state, and the output PWM signals

will stop unless special circuitry is implemented to handle this situation. To prevent the output PWM signals

from stopping in a clipping or CB3C situation, narrow pulses are injejcted to the gate drive to maintain output

frequency during this state is reduced to 1/4 of the normal switching frequency.

Signal clipping is signalled on the OTW_CLIP pin and is self clearing when signal level reduces and the

device reverts to normal operation. The OTW_CLIP pulses starts at the onset to output clipping, typically at a

THD level around 0.01%, resulting in narrow OTW_CLIP pulses starting with a pulse width of ~500ns.

Figure 19. Signal Clipping PWM and Speaker Output Signals

9.4.5.3 DC Speaker Protection

The output DC protection scheme protects a speaker from excess DC current in case one terminal of the

speaker is connected to the amplifier while the other is accidentally shorted to the chassis ground. Such a short

circuit results in a DC voltage of PVDD/2 across the speaker, which potentially can result in destructive current

levels. The output DC protection detects any unbalance of the output and input current of a BTL output (current

into/out of one halfbridge equals current out of/into the other halfbridge), and in the event of the unbalance

exceeding a programmed threshold, the overload counter increments until its maximum value and the affected

output channel is shut down. DC Speaker Protection is disabled in PBTL mode operation.