Built-in self-diagnostic features are incorporated in the TMCS1133 to warn when operating conditions invalidate current sensor measurements. Two critical conditions being monitored are sensor temperature and sensitivity.

Thermal Alert

As discussed in the Safe Operating Area section, high levels of input current can generate excessive heat inside the TMCS1133. High input currents, coupled with elevated ambient temperatures and printed circuit board thermal design can cause the TMCS1133 to overheat and be permanently damaged by exceeding maximum allowed junction temperatures. A thermal alert occurs when the internal temperature approaches the maximum allowed junction temperature.

Sensor Alert

In addition to temperature, sensor sensitivity and offset are constantly being monitored inside the TMCS1133. A sensor alert occurs in the unlikely event Hall sensor sensitivity or offset is out of range compared with factory set limits.

The active-low ALERT output signal can be used to decipher which of four diagnostic states the TMCS1133 resides. As shown in Figure 8-8, the duty cycle of the 8kHz PWM output signal indicates which, neither, or both of the thermal and sensor operating condition warnings exist.