The TPS25984, TPS25985, TPS25990, and TPS1685 eFuses respond to output over-current conditions during steady-state by performing a circuit-breaker action after a user-adjustable transient fault blanking interval. This action allows the device to support a higher peak current for a short user-defined interval but also makes sure of robust protection in case of persistent output faults.

Figure 4-1 Steady-State Over-current (Circuit-Breaker) Response

The device constantly senses the output load current and provides an analog current output (I_IMON) on the IMON pin, which is proportional to the load current. This in turn produces a proportional voltage (V_IMON) across the IMON pin resistor (R_IMON) as per Equation 1.

Where G_IMON is the current monitor gain (I_IMON : I_OUT)

The over-current condition is detected by comparing this voltage against the voltage on the IREF pin as a reference. The reference voltage (V_IREF) sets the over-current protection threshold (I_OCP) accordingly.

• In the standalone or primary mode of operation, the internal current source interacts with the external IREF pin resistor (R_IREF) to generate the reference voltage. It is also possible to drive the IREF pin from an external low impedance reference voltage source as shown in Equation 2.
  Equation 2. $V_{IREF}=I_{IREF}\times R_{IREF}$
• In a primary and secondary parallel configuration, the primary eFuse or controller drives the voltage on the IREF pin to provide an external reference (V_IREF) for all the secondary devices in the chain.

The over-current protection threshold during steady-state (I_OCP) can be calculated using Equation 3.

After an over-current condition is detected, that is the load current exceeds the programmed current limit threshold (I_OCP), but stays lower than the scalable short-circuit threshold (I_SFT) of 2 × I_OCP, the device starts discharging the ITIMER pin capacitor using an internal pull-down current (I_TIMER) of ~ 2.0μA. If the load current drops below the circuit-breaker threshold before the ITIMER capacitor discharges by ΔV_ITIMER of 1.5V (typical), the ITIMER is reset by pulling it up to V_INT of 3.65V (typical) internally and the circuit-breaker action is not engaged. This action allows short overload transient pulses to pass through the device without tripping the circuit. If the over-current condition persists, the ITIMER capacitor continues to discharge and after it falls by ΔV_ITIMER, the circuit-breaker action turns off the device immediately. At the same time, the ITIMER cap is charged up to V_INT again immediately so that it is at its default state before the next over-current event. This action makes sure the full blanking timer interval is provided for every over-current event. Equation 4 can be used to calculate the R_IMON value for the desired over-current threshold.

The duration for which transients are allowed can be adjusted using an appropriate capacitor value from ITIMER pin to ground. The transient over-current blanking interval can be calculated using Equation 5.

Figure 4-1 illustrates the over-current response for TPS25984, TPS25985, TPS25990, and TPS1685 eFuses. After the part shuts down due to a circuit-breaker fault, the part either stays latched off (latch-off variant) or restarts automatically after a fixed delay (auto-retry variant).

Figure 4-2 and Figure 4-3 represent the responses of TPS25990 eFuse to a transient overload event and a persistent overload event.

Figure 4-2: Device in steady-state, Load current ramped up from 50A to 70A for 10ms and then ramped down to 50A. OCP threshold set to 55A, Over-current blanking delay set to 15ms (OC_TIMER = 0x89)

Figure 4-3: Device in steady-state, Load current ramped up from 50A to 70A for > 15ms. OCP threshold set to 55A, Over-current blanking delay set to 15ms (OC_TIMER = 0x89)

Figure 4-2 Transient Over-Current Blanking in TPS25990 eFuse

Figure 4-3 Over-current Protection in TPS25990 eFuse