STEF05D Datasheet, PDF (9/19 Pages) STMicroelectronics – Electronic fuse for 5 V line

STEF05D
Typical application
5.1.2
5.1.3
5.1.4
5.1.5
Normal operating condition
The STEF05D E-fuse behaves like a mechanical fuse, buffering the circuitry on its output
with the same voltage shown at its input, with a small voltage fall due to the N-channel
MOSFET R_DSOn.
Output voltage clamp
This internal protection circuit clamps the output voltage to a maximum safe value, typically
6.65V, if the input voltage exceeds this threshold.
Current limiting
When an overload event occurs, the current limiting circuit reduces the conductivity of the
power MOSFET, in order to clamp the output current at the value selected externally by
means of the limiting resistor R_Limit (Figure 3).
Thermal shutdown
If the device temperature exceeds the thermal latch threshold, typically 165°C, the thermal
shutdown circuitry turns the power MOSFET off, thus disconnecting the load. The EN/Fault
pin of the device will automatically be set at an intermediate voltage, in order to signal the
overtemperature event.
From this condition the E-fuse can be reset either by cycling the supply voltage or by pulling
down the EN pin below the V_il threshold, and then releasing it.
5.2
R_Limit calculation
As shown in Figure 3, the device uses an internal N-channel sense FET with a fixed ratio, to
monitor the output current and limit it at the level set by the user.
The R_Limit value for achieving the requested current limitation can be estimated by using the
following theoretical formula, together with the graph in Figure 13:
Equation 1
RLimit = _I---_s---^4h---²-_o---_r---_t
5.3
C_dv/dt calculation
Connecting a capacitor between the C_dv/dt pin and GND will allow the modification of the
output voltage ramp time.
Given the desired time interval t during which the output voltage goes from zero to his
maximum value, the capacitance to be added on C_dv/dt pin can be calculated using the
following theoretical formula:
DocID024394 Rev 1
9/19