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TIMER

1 V/div

5 A/div

GATE 10 V/div

OUT 10 V/div

GATE 10 V/div

VCC 10 V/div

OUT 10 V/div

5A/div

TPS2490

TPS2491

SLVS503 – NOVEMBER 2003

APPLICATION INFORMATION (continued)

Figure 14. Current Limit Overview

The TPS2490/91 responds rapidly to the short circuit as seen in Figure 15. The falling OUT voltage is the result

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 15. Current Limit Onset

Minimal input voltage overshoot appears in Figure 15 because a local 100-

µF 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 distribution’s inductance. The exact waveforms seen in an

application depend upon many factors including parasitics of the voltage distribution, circuit layout, and the short

itself.

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