8.1 Overview

The TPS25925x/6x is an e-fuse with integrated power switch that is used to manage current, voltage and start-up voltage ramp to a connected load. The device starts its operation by monitoring the VIN bus. When VIN exceeds the undervoltage-lockout threshold (V_UVR), the device samples the EN/UVLO pin. A high level on this pin enables the internal MOSFET. As VIN rises, the internal MOSFET of the device starts conducting and allow current to flow from VIN to OUT. When EN/UVLO is held low (below V_ENF), internal MOSFET is turned off. User also has the ability to modify the output voltage ramp time by connecting a capacitor between dV/dT pin and GND.

After a successful start-up sequence, the device now actively monitors its load current and input voltage, ensuring that the adjustable overload current limit IOL is not exceeded and input voltage spikes are safely clamped to VOVC level at the output. This keeps the output device safe from harmful voltage and current transients. The device also has built-in thermal sensor. In the event device temperature (T_J) exceeds TSHDN, typically 150°C, the thermal shutdown circuitry shuts down the internal MOSFET thereby disconnecting the load from the supply. In TPS259250/60, the output remains disconnected (MOSFET open) until power to device is recycled or EN/UVLO is toggled (pulled low and then high). The TPS259251/61 device remains off and commences an auto-retry cycle of 145 ms after device temperature falls below T_SHDN – 10°C. This auto-retry cycle continues until the fault is cleared.

8.2 Functional Block Diagram

8.3 Feature Description

8.3.3 dV/dT

Connect a capacitor from this pin to GND to control the slew rate of the output voltage at power-on. This pin can be left floating to obtain a predetermined slew rate (minimum T_dVdT) on the output. Governing slew rate at start-up is shown in Equation 1.

Equation 1.

Where:

I_dVdT = 220 nA (TYPICAL)
C_INT = 70 pF (TYPICAL)
GAIN_dVdT = 4.85

The total ramp time (T_dVdT) for 0 to VIN can be calculated using Equation 2.

Equation 2.

For details on how to select an appropriate charging time/rate, see the applications section Setting Output Voltage Ramp Time (TdVdT).

8.3.5 ILIM

The device continuously monitors the load current and keeps it limited to the value programmed by R_ILIM. After start-up event and during normal operation, current limit is set to I_OL (over-load current limit). See Equation 3.

Equation 3.

When power dissipation in the internal MOSFET [P_D = (V_VIN – V_OUT) × I_OUT] exceeds 10 W, there is a 2% to 12% thermal foldback in the current limit value so that I_OL drops to I_SC. In each of the two modes, MOSFET gate voltage is regulated to throttle short-circuit and overload current flowing to the load. Eventually, the device shuts down due to over temperature. See Figure 39.

Figure 39. Thermal Foldback in Current Limit

During a transient short circuit event, the current through the device increases very rapidly. The current-limit amplifier cannot respond to this event because of its limited bandwidth. Therefore, the TPS25925/6 incorporates a fast-trip comparator, which shuts down the pass device when I_OUT > I_FASTRIP, and terminates the rapid short-circuit peak current. The trip threshold is set to 60% higher than the programmed over-load current limit (I_FASTRIP = 1.6 x I_OL). After the transient short-circuit peak current has been terminated by the fast-trip comparator, the current limit amplifier smoothly regulates the output current to I_OL. See Figure 40 and Figure 41.

Figure 40. Fast-Trip Current

Figure 41. Fast-Trip and Current Limit Amplifier Response for Short Circuit

8.4 Device Functional Modes

The TPS25925x/6x is a hot-swap controller with integrated power switch that is used to manage current, voltage and start-up voltage ramp to a connected load. The device starts its operation by monitoring the VIN bus. When V_VIN exceeds the undervoltage-lockout threshold (V_UVR), the device samples the EN/UVLO pin. A high level on this pin enables the internal MOSFET. As VIN rises, the internal MOSFET of the device starts conducting and allows current to flow from VIN to OUT. When EN/UVLO is held low (that is, below V_ENF), the internal MOSFET is turned off; thereby, blocking the flow of current from VIN to OUT. The user can modify the output voltage ramp time by connecting a capacitor between dV/dT pin and GND.

Having successfully completed its start-up sequence, the device now actively monitors the load current and input voltage, ensuring that the adjustable overload current limit I_OL is not exceeded and input voltage spikes are safely clamped to V_OVC level at the output. This keeps the output device safe from harmful voltage and current transients. The device also has built-in thermal sensor. If the device temperature (T_J) exceeds T_SHDN, typically 150°C, the thermal shutdown circuitry shuts down the internal MOSFET; thereby, disconnecting the load from the supply. In the TPS259250/60, the output remains disconnected (MOSFET open) until power to device is recycled or EN/UVLO is toggled (pulled low and then high). The TPS259251/61 device remains off and commences an auto-retry cycle of 145 ms after device temperature falls below T_SHDN – 10°C. This auto-retry cycle continues until the fault is cleared.