GATE10V/div
VCC10V/div
OUT10V/div
I
IN
5A/div
-
-
TIMER
1 V/div
I
IN
0.5 A/div
GATE 10 V/div
OUT 10 V/div
-
-
TPS2490
TPS2491
www.ti.com
SLVS503D NOVEMBER 2003REVISED JULY 2012
Figure 15. Current Limit Overview
The TPS2490/91 responds rapidly to the short circuit as seen in Figure 16. The falling OUT voltage is the result
of M1 and C
O
currents through the shorts impedance at this time scale. The internal GATE clamp causes the
GATE voltage to follow the output voltage down and subsequently limits the negative V
DS
to 12 V. The rapidly
rising fault current overdrives the GATE amplifier causing it to overshoot and rapidly turn M1 off by sinking
current to ground. M1 slowly turns back on as the GATE amplifier recovers; M1 then settles to an equilibrium
operating point determined by the power limiting circuit.
Figure 16. Current Limit Onset
Minimal input voltage overshoot appears in Figure 16 because a local 100-糉 bypass capacitor and very short
input leads were used. The input voltage would overshoot as the input current abruptly drops in a typical
application due to the stored energy in the input distributions inductance. The exact waveforms seen in an
application depend upon many factors including parasitics of the voltage distribution, circuit layout, and the short
itself.
Copyright ?20032012, Texas Instruments Incorporated
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