9.4.2 Thermal Overload

The AFE031 contains internal protection circuitry that automatically disables the PA output stage if the junction temperature exceeds +150°C. If a fault condition occurs that causes a thermal overload, and if the T_FLAG_EN bit (location 5 in the Control2 Register) is enabled, the T_FLAG bit (location 5 in the RESET Register) is set to a '1'. This configuration results in an interrupt signal at the INT pin. The AFE031 includes a thermal hysteresis and allows the PA to resume normal operation when the junction temperature reduces to +135°C. The T_FLAG bit remains set to a '1' even after the device returns to normal operation. The T_FLAG bit remains '1' until it is reset by the microprocessor.

If the T_FLAG_EN bit (location 5 in the Control2 Register) is disabled and a thermal overload condition occurs, the PA continues to go into thermal limit and protect the AFE031, but the contents of the T_FLAG bit (location 5 in the RESET Register) remain at the previous value (presumably '0' for normal operation), and the AFE031 does not issue an interrupt at the INT pin.

Once an interrupt is signaled (that is, INT goes low), the contents of the I_FLAG and T_FLAG bits can be read by the microprocessor to determine the type of interrupt that occurred. Using the Control2 Register, each interrupt type (current or thermal) can be individually enabled or disabled, allowing full user customization of the INT function. For proper operation of the interrupt pin it is recommended to configure the interrupt enable registers in the Control2 Register by writing to bit locations 5, 6, and 7 following the information in Table 8 after each time the AFE031 is powered on. Failure to properly configure bit locations 5, 6, and 7 after power on may result in unexpected interrupt signals.

Table 8 lists the register contents associated with each interrupt condition.

TSENSE Pin (10)

The TSENSE pin is internally connected to the anode of a temperature-sensing diode located within the PA output stage. Figure 44 shows a remote junction temperature sensor circuit that can be used to measure the junction temperature of AFE031. Measuring the junction temperature of the AFE031 is optional and not required.

Figure 44. Interfacing the TMP411 to the AFE031

Tx_FLAG (Pin 47)

The Tx_FLAG pin is an open drain output that indicates the readiness of the Tx signal path for transmission. When the Tx_FLAG pin is high, the transmit signal path is enabled and ready for transmission. When the Tx_FLAG pin is low, the transmit path is not ready for transmission.

Rx_FLAG (Pin 48)

The Rx_FLAG pin is an open drain output that indicates the readiness of the Rx signal path for transmission. When the Rx_FLAG pin is high, the transmit signal path is enabled and ready for transmission. When the Rx_FLAG pin is low, the transmit path is not ready for transmission.