The TPS2556-Q1 and TPS2557-Q1 devices respond to overcurrent conditions by limiting their output current to I_OS. On detecting an overcurrent condition, the device maintains a constant output current, and the output voltage reduces accordingly. Two possible overload conditions can occur.

The first condition is when a short circuit or partial short circuit is present on a powered-up and enabled device. With the output voltage held near zero potential with respect to ground, the TPS2556-Q1 or TPS2557-Q1 device ramps the output current to I_OS. The TPS2556-Q1 and TPS2557-Q1 devices limit the current to I_OS until removal of the overload condition or until the device begins to cycle thermally.

The second condition is when a short circuit, partial short circuit, or transient overload occurs while the device is enabled and powered on. The device responds to the overcurrent condition within time t_(IOS) (see Figure 8-2). Overdriving the current-sense amplifier during this time and momentarily disables the internal N-channel MOSFET. The current-sense amplifier recovers and ramps the output current to I_OS. Similar to the previous case, the TPS2556-Q1 and TPS2557-Q1 devices limit the current to I_OS until removal of the overload condition or until the device begins to cycle thermally.

The TPS2556-Q1 and TPS2557-Q1 cycle thermally if an overload condition is present long enough to activate thermal limiting in any of the above cases. The device turns off when the junction temperature exceeds 135°C (minimum) while in current limit. The device remains off until the junction temperature cools 20°C (typical) and then restarts. The TPS2556-Q1 and TPS2557-Q1 cycle on and off until removal of the overload (see Figure 10-7).