During an output short-circuit event, the current through the device increases very rapidly. When an output short-circuit is detected, the internal fast-trip comparator triggers a fast protection sequence to prevent the current from building up further and causing any damage or excessive input supply droop. The fast-trip comparator employs a scalable threshold (I_SFT) which is equal to 2 × I_OCP (primary device) or 2.25 × I_OCP (secondary device) during steady-state and 1.5 × I_LIM during inrush. This action enables the user to adjust the fast-trip threshold as per system rating, rather than using a high fixed threshold which can not be suitable for all systems. After the current exceeds the fast-trip threshold, the TPS25985x turns off the FET within t_SFT. The device also employs a higher fixed fast-trip threshold (I_FFT) to provide fast protection against hard short-circuits during steady-state (FET in linear region). After the current exceeds I_FFT, the FET is turned off completely within t_FFT. Figure 8-5 illustrates the short-circuit response for TPS25985x eFuse.

In some of the systems, for example blade servers and telecom equipment which house multiple hot-pluggable blades or line cards connected to a common supply backplane, there can be transients on the supply due to switching of large currents through the inductive backplane. This can result in current spikes on adjacent cards which can potentially be large enough to trigger the fast-trip comparator of the eFuse. The TPS25985x uses a proprietary algorithm to avoid nuisance tripping in such cases thereby facilitating uninterrupted system operation.

Figure 8-5 Short-Circuit Response