STEF12H60MPUR datasheet(13/34 Pages) STMICROELECTRONICS

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Device functional description

The STEF12H60M is a 12 V electronic fuse (eFuse), which is able to limit the current during fault events, such as

output overload or short-circuit.

The current limiting loop is also used during the start-up phase of the eFuse to avoid startups into faulty loads.

During normal operation, the eFuse works as a low-resistance power switch, therefore the output voltage follows

the input one. In case of overcurrent event, the eFuse limits the VGS of the internal MOSFET switch, in order to

clamp the output current to a safe value.

If the fault persists, after a predefined safety timer, or in case the die temperature hits the thermal protection

threshold, due to the increased power dissipation, the device goes into shutdown, the internal switch is turned off

and the load is disconnected from the power supply. The device is latched in this off-state until a power supply

re-cycle is performed. The auto-retry version instead, is able to re-try starting the device after a fault event, with a

typical delay of 1 ms.

The current limit and soft-start features are programmable by the user, through external components.

6.1

UVLO ON/PD function

The device is supplied through the VIN pins, which carry the power directly to the internal power MOSFET drain

connection, and the VINF pin, which is the input of the internal regulator, used to supply the analog and logic

circuits. This pin must be connected externally to VIN through an R-C filter (see Section 3 Typical application).

The UVLO (undervoltage lockout) monitors the voltage of the internally regulated VDD node and turns on the

device when VDD > VDD_ON (typically 4.3 V). If VDD falls below the UVLO hysteresis threshold (VDD < VDD_OFF),

the device is turned off including the reset of fault state.

6.2

ON/PD function

During turn-on, provided that the UVLO rising threshold has been surpassed, the start-up procedure begins once

the device is enabled via the ON/PD pin. The ON/PD is a logical input with a dual functionality, according to the

following description:

Enable/disable the device: when VON/PD > VON, the device is enabled. If VON/PD is pulled down to VOFF or

a lower voltage, the device is disabled and the output is shut down. In case the shutdown occurred due to a

fault (thermal, overcurrent, failed startup), the device cannot be turned on again via the ON/PD pin. To reset

the device from this latched status, a power supply re-cycle is necessary. Alternatively, a reset can be forced

without turning off the power supply, by pulling VDD pin below the UVLO voltage and then releasing it.

Activate/deactivate the output discharge feature (PD – output pulldown): if VON/PD is kept between VPD (typ.

0.8 V) and VOFF (typ. 1.2 V) for at least 2 ms (tPD), the integrated 0.77 kΩ RPD discharging resistor is

connected between VOUT and GND

The ON/PD pin has an internal pull-up current generator connected to the internal LDO, therefore, if the pin is not

connected to an external controller IC, it goes to the ON-state (device enabled).

The 5 µA ON/PD bias current can be used to charge an external capacitor; in this manner prolonging the initial

delay time, defined as the time interval between power supply reaching the UVLO threshold and the output

voltage controlled ramp-up initialization.

6.3

Soft-start

The device provides monotonic, controlled start-up ramp, in order to keep the inrush current under control. The

output voltage rise time can be set by an external CSS, which is charged with a constant current during the start-

up phase. The soft-start range is adjustable from 1 to 100 ms.

Given the required ramp-up time, the CSS capacitance can be calculated according to the following equation:

CSS=N× tSS×ISS×10

VIN

(1)

where VIN is typically 12 V, tSS is in the 10-100 ms range and N is the number of eFuses in parallel.

STEF12H60M

Device functional description

DS13608 - Rev 3

page 13/34

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