SLVSFZ1 December 2020 TPS27SA08-Q1
Figure 10-4 shows the behavior of the TPS27SA08-Q1 device in this application when the MCU provides an enable pulse to beginning heating the resistive element. Shortly after the EN pin goes high, the load current begins to flow and the SNS pin measures the output current.
By measuring the voltage on the SNS pin, the TPS27SA08-Q1 device can communicate back to the system MCU what the load current is. Figure 10-5 shows that when the seat heater approaches full load and IOUT jumps from a low load current of 1 A up to a 5-A load current, the load step is mirrored on the SNS pin.
One common concern in these type of applications is that the heating element can accidentally lose connection, creating an open load situation. In this case, it is ideal for the TPS27SA08-Q1 device to recognize that the load has been removed and report a FLT to the MCU. Figure 10-6 shows the behavior of the TPS27SA08-Q1 device when there is no load attached. As soon as the DIAG_EN pin is engaged, the SNS output goes high and the ST output engages low. By monitoring these pins, the MCU can recognize there is a fault and notify the user that maintenance is required.
Importantly, the TPS27SA08-Q1 device will also protect the system in the event of a short-circuit. Figure 10-7 shows the behavior of the device if it is enabled into a short circuit condition. The current will be clamped to near the current limit threshold (ICL) until it hits an over temperature event, at which point the FET will be turned off. In this way, the system is protected from unchecked overcurrent in the event of a short circuit.