Datasheet AP2337 (Diodes) - 7

AP2337 1.0A SINGLE CHANNEL CURRENT-LIMITED LOAD SWITCH Application Note Protection Features: Under-voltage Lockout (UVLO)
Whenever the input voltage falls below UVLO threshold (~2.5V), the power switch is turned off. This facilitates the design of hot-insertion systems where it is not possible to turn off the power switch before input power is removed.
Over-current and Short Circuit Protection
An internal sensing FET is employed to check for over-current conditions. Unlike current-sense resistors, sense FETs do not increase the series resistance of the current path. When an overcurrent condition is detected, the device maintains a constant
T
output current and reduces the output voltage accordingly. Complete shutdown occurs only if the fault stays long enough to activate thermal limiting.
UC
The different overload conditions and the corresponding response of the AP2337 are outlined below:
NO Conditions Explanation Behavior of the AP2337
Output is shorted before The IC senses the short circuit and immediately Short circuit condition at input voltage is applied or 1 clamps output current to a certain safe level
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start-up before the part is powered namely I up. short • At the instance the overload occurs, higher current may flow for a very short period of Short-Circuit or Overload time before the current limit function can Short-circuit or condition that occurs when react. 2 Overcurrent condition the part is powered up and • After the current limit function has tripped above UVLO. (reached the over-current trip threshold), the device switches into current limiting mode and the current is clamped at Ishort /ILIMIT. Gradual increase from Load increases gradually The current rises until ILIMIT. Once the threshold 3 nominal operating current until the current-limit has been reached, the device switches into its to ILIMIT threshold. current limiting mode and is clamped at ILIMIT.
Reverse Current Protection
The USB specification does not allow an output device to source current back into the USB port. In a normal MOSFET switch, current will flow in reverse direction (from the output side to the input side) when the output side voltage is higher than the input side. A
reverse current limit
feature is implemented in the AP2337 to limit such back currents. This circuit is activated by the difference between the output voltage and the input voltage (100mV TYP). After the reverse current circuit has tripped (reached the reverse current trip threshold), the current rises until IROCP level. When the fault exists for more than 600us, output device is disabled and shutdown. This is called the "Deglitch time from reverse current trigger to MOSFET turn off”. Recovery from IROCP occurs when the output voltage falls to 101% of input voltage.
Over-Voltage Protection
The device has an
output over-voltage
protection that triggers when the output voltage reaches 114% (TYP) of input voltage. When this fault condition stays on for longer than 15us (This is called the “Debounce time from output over-voltage to MOSFET turn off” ) output device is disabled and shutdown. Recovery from ROVP occurs when the output voltage falls to 101% of input voltage. AP2337 7 of 10 October 2011 Document number: DS35060 Rev. 2 - 2
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