4 TVS-less ideal diode: mode of operation and working principle

During VDS clamp operation, there is current conduction from the output capacitors back to the input source. This operation is acceptable during an ISO 7637-2 Pulse 1 transient event, where the output voltage holdup requirement is not mandatory given the long brownout duration of 200 ms. However, reverse-current protection is a critical feature needed in system tests, where the supply interruptions are for short durations such as an input micro short (LV124-E10) as well as during AC superimposed testing (LV124-E06). The VDS clamp operation should not engage during these tests, ensuring reverse-current protection.

Figure 4-1 is a flow chart that can help you decide the VDS clamp threshold to ensure EMC performance across various test conditions.

For a TVS-less ideal diode controller, when the input voltage is lower than the output voltage but has not reached the VDS clamp threshold, the ideal diode controller remains in reverse-current blocking mode and the external FET remains off, in order to ensure that the output voltage does not drop much from its nominal value. This mode of operation is preferable in system-level EMC tests with output-voltage holdup requirements such as input micro-short interruptions (LV124-E10, ISO 16750-2). When the voltage difference between the output and input exceeds the VDS clamp threshold, such as in the case of an ISO 7637-2 Pulse 1 transient event, the ideal diode controller enables the gate drive and the external FET operates in the saturation region, acting as a current source. The output capacitor provides reverse energy back to the input source and the output voltage drops from its nominal value. Figure 4-2 shows the equivalent circuit of ideal diode controller TVS-less operation during an ISO 7637-2 Pulse 1 transient event.

Section 5 and Section 6 discusses external component selection considerations.