During the power-up sequence, the circuit monitoring the AVDD pin (UVLO) will hold the device in reset (including all configuration registers) until the supply is valid. The device will not exit hardware shutdown until AVDD is valid and the SDZ pin is released. Once SDZ is released, the digital core voltage regulator will power up, enabling detection of the operational mode. If AVDD dips below the UVLO threshold, the device will immediately be forced into a reset state.

The device also monitors the PVDD supply and holds the analog core in power down if the supply is below the UVLO threshold (set by register bits PVDD_UVLO_TH[5:0]). If the TAS2764 is in active operation and an UVLO fault occurs, the analog blocks will immediately be powered down to protect the device. These faults are latched and require a transition through HW/SW shutdown to clear the fault. The latched registers will report UVLO faults.

The device transitions into software shutdown mode if it detects any faults with the TDM clocks such as:

? Invalid SBCLK to FSYNC ratio

? Invalid FSYNC frequency

? Halting of SBCLK or FSYNC clocks

Upon detection of a TDM clock error, the device transitions into software shutdown mode as quickly as possible to limit the possibility of audio artifacts. Once all TDM clock errors are resolved, the device volume ramps back to its previous playback state. During a TDM clock error, the IRQZ pin will assert low if the clock error interrupt mask register bit IM_TDMCE is set low. The clock fault is also available for read-back in the latched fault status registers (bits IL_TDMCE and IR_TDMCE]). Reading the latched fault status register clears the register.

The TAS2764 also monitors die temperature and Class-D load current and will enter software shutdown mode if either of these exceed safe values. As with the TDM clock error, the IRQZ pin will assert low for these faults if the appropriate fault interrupt mask register bit is set low for over temperature and for over current. The fault status can also be monitored in the latched fault registers as with the TDM clock error.

Over temperature warnings and flags are not raised if the device is in Idle or Noise Gate mode.

The status registers (and IRQZ pin if enabled via the status mask register) also indicate limiter behavior including when the limiter is activated, when PVDD is below the inflection point, when maximum attenuation has been applied, when the limiter is in infinite hold and when the limiter has muted the audio.

In the situations when the device operates in PWR_MODE2 or PWR_MODE4, the VBAT1S pin is supplied by an internal LDO. Protection circuits monitor this block and generate faults in case of under voltage, over voltage or if the LDO is over loaded. There is no re-try if one of these faults triggers; the device goes into shut down and the IRQZ pin will go low.

The IRQZ pin is an open drain output that asserts low during unmasked fault conditions and therefore must be pulled up with a resistor to IOVDD. An internal pull up resistor is provided in the TAS2764 and can be accessed by setting the IRQZ_PU register bit high. Figure 8-12 below highlights the IRQZ pin circuit.

Figure 8-12 IRQZ Pin

The IRQZ interrupt configuration can be set using IRQZ_PIN_CFG[1:0] register bits. The IRQZ_POL register bit sets the interrupt polarity and IRQZ_CLR register bit allows to clear the interrupt latch register bits.

Live flag registers are active only when the device is in active mode of operation. If the device is put in shutdown by I²C command or due to any fault condition described below, the live flags will be reset. Latched flags will not be reset in this condition and available for user to read their status.