Features: 1.8 to 5.5V Input Voltage Range Control Turn On 200MA Current Limit Option Under Voltage Lockout Thermal Shutdown <2µA Shutdown Current Fast Current Limit Response Time 5µs to Moderate Over Current 30ns Fault Blanking

Application: PDA Mobile Phone GPS Device MP3 Player Digital Camera Peripheral Port Hot Plug Supplies General Description: It is a load switch for systems and load conditions that may encounter high current. These devices contain 0.12Ω current limiting p-channel MOSFETs that can operate at input voltages ranging from 1.8-5.5V. The switch control can interface directly with the low voltage control signal through the logic input (ONB). This part contains thermal shutdown protection that shuts down when a continuous current is too large causing overheating. Operates in constant current mode when the switch current reaches the current limit to prevent excessive current that can cause damage. For the fpf2148, the current limit condition will immediately pull the fault signal pin low and the part will remain in constant current mode until the switch current falls below the current limit. The minimum current limit is 200mA. The part is housed in a space saving 6-pin 2x2 MLP package.

Instructions

The FPF2148 is a current limit switch designed to protect systems and potentially high current applications. At the heart of each device is a 0.12Ω p-channel MOSFET and controller with a wide input operating range of 1.8-5.5V. Controller protection prevents system failures with current limiting, undervoltage lockout, thermal shutdown, and power good features. The current limit is preset to 200mA. The on/off control onb pin controls the state of the switch. Activating ONB continuously (ONB pin low) keeps the switch ON so that the temperature exceeds 140°C as long as there is no undervoltage on the VIN or connector. The ONB activates the LO and has a low threshold enabling it to interface with low voltage signals. Additionally, excessive current can cause the switch to shut down due to thermal shutdown. The FPF2148 does not spin to shut down in overcurrent conditions, but remains operating in constant current mode with thermal shutdown or undervoltage lockout active as long as the ONB is active.

The ON pin controls the voltage and VIN pin independently recommended operating ranges. The ON pin voltage can be driven by a voltage level higher than the input voltage. Fault reporting When overcurrent, input undervoltage, or overtemperature is detected, the signal lamp signals a fault to activate LO mode. The flag fell immediately. It will remain low for the duration of the fault and immediately return high to end the fault state. FlagB is an open-drain output which requires a pull-up resistor between VIN and FlagB. During shutdown, disable the drop-down menu on flag B to reduce the current consumption of the power supply. Current Limit The current limit ensures that the current through the switch does not exceed 400mA, but is not limited to less than 200mA. The FPF2148 has no current limit blanking period, so the current limit condition flag B is activated immediately. The part will remain in constant current state until the ONB pin is turned off or thermal shutdown turns off the switch. Undervoltage lockout if the input voltage falls below the undervoltage lockout threshold.

In conjunction with ONB pin activation, the input voltage rises above the undervoltage lockout threshold and will cause the switch to be turned on in a controlled manner which limits current overcurrent. Thermal Shutdown Thermal shutdown protects the mold from excessively high temperatures generated internally or externally. In an overtemperature condition, flag B is activated and the switch is closed. If the mold temperature drops below the threshold temperature. Power Well The FPF2148 has a "Power Well" feature. The pgood pin is an open-drain mosfet, when the output voltage reaches 90% of the input voltage. When there is no battery in the load, the PGood pin requires an external pull-up resistor connected to the output voltage side and logic level enable of the subsequent controller. This will provide a logic level PGood similar to a CMOS output stage, while still retaining the option to connect the pull-up to a different supply voltage. A 100kΩ pull-up resistor is recommended. The pgood pin state is independent of the open pin position. This means when the load switch is open. If the power good function is not used for the application the pins can be connected directly to GND.

Input capacitors limit the input supply voltage drop caused by transients Inrush current when the switch is turned on to discharge the load capacitors or short circuits, a capacitor needs to be placed between the VIN and ground. The 4.7µf ceramic capacitor CIN must be close to the VIN. Higher CIN values can be used to further reduce the switch voltage drop into a large capacitive load. The output capacitor should be at vout and ground. This capacitor prevents parasitic plate inductance from driving the output voltage below ground when the switch is open. For the fpf2148, the total output capacitance needs to be kept at the maximum value, CUT(max), to prevent the part from registering an overcurrent condition and closing the switch. The maximum output capacitance can be determined by following the formula, Power dissipation During normal operation of the switch, power dissipation is small for the part. Parts with higher current limit will dissipate the most powerful force will only be If the part goes into current limit, the maximum power dissipation occurs when the output is shorted to ground. For the FPF2148, an output short circuit will cause the part to be in a constant current state, and in the worst case, the power dissipation is calculated in (3) until thermal shutdown is activated. At that time it will be as long as the ONB pin is valid and there is a short circuit. Board Layout For best performance, all traces should be as short as possible. To be most effective, input and output capacitors should be placed close to the device to minimize the effects of parasitics during normal and short-circuit operation that may have slight inductance. Using wide traces for VIN (vin), VIN (vout), and ground (gnd) will help minimize parasitic electrical effects while minimizing the thermal impedance of the enclosure to the environment. The middle pad (pin 7) should be connected to the ground plane for improved thermal performance of the load switch. Improper layout can cause junction temperature rise and trigger thermal shutdown protection. This problem is worst case when the switch is in an overcurrent state or the output is shorted to ground.

Sequential Startup Sequential startup is achieved using the power good pin which can be connected to the enable pin of another active high level load switch. When the load switch is off, the PGOOD pin is asserted low. This feature allows subsequent circuits to be driven. The diagram above illustrates the power good feature of sequential startup. As the fpf2148's vout1 starts ramping to 90% of its input voltage active high switch remains off. Given that VOUT1 passes the 90% threshold, the power good signal becomes active and claims high. This signal will turn on the active high load switch and VOUT2 will begin to increase. This total startup time may vary depending on the supply voltage used in the application.