STEF4S Datasheet, PDF (9/22 Pages) STMicroelectronics – Electronic fuse for 3.3 V and 5 V lines

STEF4S
Typical characteristics
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
Operating modes
Turn-on
When the input voltage is applied and the EN pin is high, the output voltage is supplied with
a slope defined by the internal dv/dt circuitry. If no additional capacitor is connected to C_SS
pin, the total time from the enable signal going high and the output voltage reaching the
nominal value is around 0.6 ms.
Normal operating condition
The STEF4S E-fuse behaves like a mechanical fuse, buffering the circuitry on its output with
the same voltage shown at its input, apart from a small voltage fall due to the MOSFET
R_DS(on).
Output voltage clamp
The internal voltage clamp circuit clamps the output voltage to the V_Clamp values reported in
Table 5 if the input voltage exceeds the typical thresholds of 3.8 V in the 3.3 V mode and 5.7
V in the 5 V mode.
Current limiting
When an overload event occurs, the current limiting circuit reduces the conductivity of the
power MOSFET, in order to clamp the input current at the pre-programmed value. The
current limit circuit has a foldback characteristic to reduce the power dissipation over the
power MOSFET in short-circuit condition.
Thermal shutdown and auto-retry function
If the device temperature exceeds the thermal shutdown threshold, typically 140 °C, the
thermal shutdown circuitry turns the power MOSFET off and disconnects the load. Once the
die temperature has decreased about 20 °C the device automatically attempts to apply
again the power to the load (auto-retry). This cycle persists until the fault condition is
removed.
5.2
Startup time and C_SS calculation
Connecting a capacitor between the C_SS pin and GND allows the modification of the output
voltage startup time.The startup time (T_ss) is defined as the time interval between the device
UVLO threshold, which has been overcome, and V_{OUT ,} which has reached 90% of the
nominal value as shown in Figure 4.
The below Table 6 shows the typical startup time obtained with the industry-standard values
of C_SS.
Parameter
Table 6. Startup time vs. C_ss capacitor value
Value
C_ss [nF]
None
10
47
100
T_ss [ms]
0.6
2.3
10.8
23
DocID025259 Rev 2
9/22
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