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FPF2143 Datasheet(PDF) 9 Page - Fairchild Semiconductor |
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FPF2143 Datasheet(HTML) 9 Page - Fairchild Semiconductor |
9 / 13 page 9 www.fairchildsemi.com FPF2140/42/43/44/46/47 Rev. D Description of Operation The FPF2140/42/43/44/46/47 are current limited switches that protect systems and loads which can be damaged or disrupted by the application of high currents. The core of each device is a 0.12Ω P-channel MOSFET and a controller capable of functioning over a wide input operating range of 1.8-5.5V. The controller protects against system malfunctions through current limiting, undervoltage lockout and thermal shutdown. The current limit is preset for either 200mA or 400mA. On/Off Control The ON pin controls the state of the switch. Activating ON continuously holds the switch in the on state so long as there is no undervoltage on VIN or a junction temperature in excess of 140°C. ON is active HI and has a low threshold making it capable of interfacing with low voltage signals. In addition, excessive currents will cause the switch to turn off for FPF2140/ 42 and FPF2144/46. The FPF2140/44 have an Auto-Restart feature which will automatically turn the switch on again after 450ms. For the FPF2142/46, the ON pin must be toggled to turn-on the switch again. With no auto-restart, the FPF2143/47 do not turn off in response to a over current condition but instead remain operating in a constant current mode so long as ON is active and the thermal shutdown or undervoltage lockout have not activated. Fault Reporting Upon the detection of an over-current, an input undervoltage, or an over-temperature condition, the FLAGB signals the fault mode by activating LO. For the FPF2140/42/44/46, the FLAGB goes LO at the end of the blanking time while FLAGB goes LO immediately for the FPF2143/47. FLAGB remains LO through the Auto-Restart Time for the FPF2140/44. For the FPF2142/ 46, FLAGB is latched LO and ON must be toggled to release it. With the FPF2143/47, FLAGB is LO during the faults and immediately returns HI at the end of the fault condition. FLAGB is an open-drain MOSFET which requires a pull-up resistor between VIN and FLAGB. During shutdown, the pull-down on FLAGB is disabled to reduce current draw from the supply. Current Limiting The current limit guarantees that the current through the switch doesn't exceed a maximum value while not limiting at less than a minimum value. For the FPF2140/42/43 the minimum current is 200mA and the maximum current is 400mA and for the FPF2144/46/47 the minimum current is 400mA and the maximum current is 800mA. The FPF2140/42/44/46 have a blanking time of 30ms, nominally, during which the switch will act as a constant current source. At the end of the blanking time, the switch will be turned-off and the FLAGB pin will activate to indicate that current limiting has occurred. The FPF2143/47 have no current limit blanking period so immediately upon a current limit condition FLAGB is activated. These parts will remain in a constant current state until the ON pin is deactivated or the thermal shutdown turns-off the switch. For preventing the switch from large power dissipation during heavy load a short circuit detection feature is introduced. Short circuit condition is detected by observing the output voltage. The switch is put into short circuit current limiting mode if the switch is loaded with a heavy load. When the output voltage drops below VSCTH, short circuit detection threshold voltage, the current limit value re-conditioned and short circuit current limit value is decreased to 62.5% of the current limit value. This keeps the power dissipation of the part below a certain limit even at dead short conditions at 5.5V input voltage. The VSCTH value is set to be 1V. At around 1.1V of output voltage the switch is removed from short circuit current limiting mode and the current limit is set to the current limit value. Undervoltage Lockout The undervoltage lockout turns-off the switch if the input voltage drops below the undervoltage lockout threshold. With the ON pin active the input voltage rising above the undervoltage lockout threshold will cause a controlled turn-on of the switch which limits current over-shoots. Reverse Current Blocking The entire FPF2140/47 family has a Reverse Current Blocking feature that protects input source against current flow from output to input. For a standard USB power design, this is an important feature which protects the USB host from being damaged due to reverse current flow on VBUS. The reverse current blocking feature is active when the load switch is turned off. If ON pin is LO and output voltage become greater than input voltage, no current can flow from the output to the input . The FLAGB operation is independent of the Reverse Current blocking feature and will not report a fault condition if this feature is activated. Thermal Shutdown The thermal shutdown protects the die from internally or externally generated excessive temperatures. During an over-temperature condition the FLAGB is activated and the switch is turned-off. The switch automatically turns-on again if temperature of the die drops below the threshold temperature. |
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