ISL6140 Datasheet, PDF (16/19 Pages) Intersil Corporation – Negative Voltage Hot Plug Controller

ISL6140, ISL6150
Inrush Current
In the example in Figure 26, the supply voltage is 48V
and the load resistor (RL) is 620Ω, for around 80mA.
The load capacitance is 100μF (100V). The Sense
Resistor (R₁) is 0.02Ω (trip point at 2.5A; well above
the inrush current here).
Note that the load current starts at 0 (FET off); reaches
a peak of ~850mA as the GATE voltage ramps and
turns on the FET slowly, and then settles out at 80mA,
once the CL is fully charged to the 48V. The width of
the inrush current pulse is 8ms wide. For comparison,
with the same conditions, but without the
gate-controlled FET, the current was over 20A, during a
130µs pulse.
OV = 54V
UV = 38V
V_DD
OFF
13V
ON
OFF
GATE
V_DD = 60V
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4₄8₈V_V
GGAATTEE
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FIGURE 26. INRUSH CURRENT
Power Supply Ramp
Figure 27 shows the power supply voltage (to the V_DD
pin, with respect to GND at the V_EE pin) ramping up. In
this case, the values chosen were R₄ = 562k;
R5 = 5.9k; R₆ = 13.3k; that sets the UV trip point
around 38V, and the OV trip point to 54V. Note that the
GATE starts at 0V, and stays there until the UV trip
point (38V) is exceeded; then it ramps (slowly, based
on the external components chosen) up to around 13V,
where it is clamped; it stays there until the power
supply exceeds the OV trip point at 54V (the GATE
shut-off is much faster than the turn-on). The total
time scale is 2 seconds; the V_DD ramp speed was
simply based on the inherent characteristic of the
particular power supply used.
FIGURE 27. POWER SUPPLY RAMP
Overcurrent at 2.3A
In Figure 28, an Electronic Load Generator was used to
ramp the load current; no load resistor or capacitor
was connected. The sense Resistor R₁ is 0.02Ω; that
should make the nominal overcurrent trip point 2.5A.
The GATE is high (clamped to around 13V), keeping
the FET on, as the current starts to ramp up from zero;
the GATE starts to go low (to shut off the FET) when
the load current hits 2.3A. Note that it takes only 44µs
for the GATE to shut off the FET (when the load current
equals zero).
Keep in mind that the tolerance of the sense resistor
(1% here) and the IC overcurrent trip voltage (V_CB)
affect the accuracy of the trip point; that’s why the trip
point doesn’t necessarily equal the 2.5A design target.
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GATE
GATE
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4^N8^OV^CAP
No cap
FIGURE 28. OVERCURRENT AT 2.3A
16
FN9039.4