Applications information

STA533WF

8/15

Doc ID 17658 Rev 2

Protection circuits

The STA533WF includes protection circuitry for overcurrent and thermal overload

conditions. A thermal warning pin (THWARN) is activated low (open-drain MOSFET) when

the IC temperature exceeds 130 °C, which is in advance of the thermal shutdown protection.

When a fault condition is detected an internal fault signal acts to immediately disable the

output power MOSFETs, placing both H-bridges in the high-impedance state. At the same

time an open-drain MOSFET connected to pin FAULT is switched on.

There are two possible modes subsequent to activating a fault:

●

Shutdown mode:

with pins FAULT (with pull-up resistor) and TRISTATE independent, an activated fault

disables the device, signalling low at pin FAULT.

The device may subsequently be reset to normal operation by toggling pin TRISTATE

from high to low and back to high using an external logic signal.

●

Automatic recovery mode:

This is shown in the applications circuit in Figure 6 and Figure 7 on page 10.

Pins FAULT and TRISTATE are shorted together and connected to a time constant

circuit comprising R59 and C58.

An activated fault forces a reset on pin TRISTATE causing normal operation to resume

following a delay determined by the time constant of the circuit.

If the fault condition is still present this operation continues to repeat until the fault

condition is removed.

An increase in the time constant of the circuit produces a longer recovery interval.

Care must be taken in the overall system design so as not to exceed the protection

thresholds under normal operation.

Power outputs

The STA533WF power and output pins are duplicated to provide a low-impedance path for

the device bridged outputs. All duplicated power, ground and output pins must be connected

for reliable operation.

Pins PWRDN or TRISTATE should be used to set all MOSFETS to the high-impedance

state during power-up and until the logic power supply on pin VL has settled.

Parallel-output and high-current operation

When using FFX mode, the STA533WF outputs can be connected in parallel to increase the

output current capability. In this configuration the device can provide 40 W into 4

Ω.

combined to give INLA = INLB and INRA = INRB, then the corresponding outputs can be

shorted together to give OUTLA = OUTLB and OUTRA = OUTRB.

The snubber RC network shown in the applications figures must be placed as close as

possible to the output pins. This reduces ringing, over- and undervoltage effects, and

improves the audio quality and EMI performance.