6

Device functional description

The STEF512GR embeds a 5 V and a 12 V electronic fuse (e-fuses). Each e-fuse is an intelligent load switch,

which is able to limit the voltage or the current during fault events, such as: input overvoltage or output overload

respectively. For this purpose, it contains 2 analogue control loops, the former limits the output voltage and the

latter limits the input current.

The current limiting loop is also used during the start-up phase of the E-fuse to limit the inrush current into the

output capacitor.

During the normal operation, the e-fuse behaves like a low-resistance Power FET, therefore the output voltage

order to clamp the output voltage or current respectively. During such events the die temperature rises due to the

power dissipation and so, if the fault persists and the overtemperature threshold is overcome, the device goes into

thermal shutdown, the internal FET is turned-off and the load disconnected from the power supply.

Once the e-fuse is in thermal shutdown, it does not restart automatically. The e-fuse can be restarted manually by

toggling the EN pin or performing a power-up cycle, (this becomes effective as soon as the die temperature drops

by at least the overtemperature hysteresis).

Each e-fuse provides factory-trimmed undervoltage lockout feature and user-adjustable output voltage rise time.

6.1

Undervoltage lockout

The undervoltage lockout circuit prevents each e-fuse from turning on if the supply voltage is below the UVLO

relevant channel is turned off.

If the supply voltage comes back into the operative range, the relevant channel restarts with a soft-start cycle.

6.2

Start-up sequence and voltage clamp

The typical start-up sequence of each e-fuse is as follows:

•

•

The disable pin is asserted by the user to low logic level (or left floating), enabling the device

•

Typically, 1.2 ms after the e-fuse starts ramping up the output voltage

•

•

this state until it hits its overtemperature threshold and shuts down.

6.3

Current limit function

Each e-fuse provides 2 kinds of current limit protections:

•

(typ.) for the 12 V one.

•

In case of strong overload or short-circuit, the short-circuit current limit is activated and the current is

STEF512GR

Device functional description

DS13212 - Rev 2

page 8/22