LM5050Q1MK-1/NOPB

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1. Describe

When connected in series with the power supply, the high-side OR-ing FET controller operates as an ideal diode rectifier along with the external MOSFET. This ORing controller allows MOSFETs to replace diode rectifiers in power distribution networks, reducing power losses and voltage drops. The LM5050Q1MK-1/NOPB controllers provide charge pump gate drive for external N-channel MOSFETs and fast response comparators to turn off the FETs when current flows in reverse. The LM5050Q1MK-1/NOPB accepts power supplies from 5 V to 75 V and can withstand transients up to 100 V. Blocking diodes are usually placed in series with the power input for ORing of redundant power supplies source and prevent supply reversals. The LM5050 replaces the diodes in these applications with NMOSFETs to reduce the voltage drop and power losses associated with passive solutions. The LM5050 operates from 5 V to 75 V, and it can withstand an absolute maximum of up to 100 V without damage. In addition to MOSFET Q1, several external components are included. Ideal diodes, like their non-ideal counterparts, exhibit something called reverse recovery. Combined with parasitic or intentionally introduced inductance, ideal diodes can experience reverse recovery spikes during reverse current turn-off. D1, D2, and R1 prevent these spikes that might otherwise exceed the LM5050's 100V survival rating. COUT is also used to absorb reverse recovery energy. Spikes and protection schemes are discussed in detail in the Short-Circuit Fault Input Power section.

2. Feature

    1. Available in standard and AEC-Q100 qualified versions LM5050Q0MK-1 (up to 150°C TJ) and LM5050Q1MK-1 (up to 125°C TJ)

    2. Functional safety capabilities

        – Documentation available to aid in functional safety system design

    3. Wide operating input voltage range, VIN: 1 V to 75 V (VBIAS required for VIN < 5 V)

    4. 100V transient capability

    5. Charge pump gate driver for external N-channel MOSFET

    6. Fast 50ns response to current reversal

    7. 2A peak gate off current

    8. Minimum VDS clamp for faster turn-off

    9. Package: SOT-6 (thin SOT-23-6)

3. Function description

1. IN, GATE and OUT pins

On initial power-up, load current will flow from source to drain through the body diode of the MOSFET. Once the voltage across the body diode exceeds VSD(REG), the LM5050-1 begins charging the MOSFET gate through a 32 µA (typ) charge pump current source. In forward operation, the gate of the MOSFET is charged until the clamping voltage of the LM5050-1's internal 12V GATE to IN pin Zener diode is reached. The LM5050-1 is designed to regulate MOSFET gate-source voltage. If the MOSFET current drops below the VSD(REG) voltage regulation point where the voltage across the MOSFET falls below 22 mV (typ), The GATE pin voltage will decrease until the voltage across the MOSFET stabilizes at 22 mV. If the source-drain voltage is greater than the VSD(REG) voltage, the gate-to-source voltage will increase and eventually reach the 12V GATE to IN pin Zener clamp level. If the MOSFET current is reversed, possibly due to an input power failure that makes the voltage on the LM5050-1 IN and OUT pins more negative than the VSD(REV) voltage of -28 mV (typ), the LM5050-1 will pass the strong GATE to IN pin discharge transistor to quickly discharge MOSFET gate. If the input supply fails suddenly, as if the supply were shorted directly to ground, reverse current will flow through the MOSFET temporarily until the gate is fully discharged. This reverse current comes from the load capacitance and the parallel supply. The LM5050-1 typically responds to a voltage reversal condition within 25 ns. bill ual time required to turn off the MOSFET will depend on the charge held by the gate capacitance of the MOSFET being used. A MOSFET with 47 nF of effective gate capacitance can be turned off in typically 180 ns. This fast turnoff time minimizes voltage disturbances at the output, as well as the current transients from the redundant supplies.

2. VS Pin

The LM5050-1 VS pin is the main supply pin for all internal biasing and an auxiliary supply for the internal gate drive charge pump. For typical LM5050-1 applications, where the input voltage is above 5 V, the VS pin can be connected directly to the OUT pin. In situations where the input voltage is close to, but not less than, the 5 V minimum, it may be helpful to connect the VS pin to the OUT pin through an RC Low-Pass filter to reduce the possibility of erratic behavior due to spurious voltage spikes that may appear on the OUT and IN pins. The series resistor value should be low enough to keep the VS voltage drop at a minimum. A typical series resistor value is 100 Ω. The capacitor value should be the lowest value that produces acceptable filtering of the voltage noise. If Vs is powered while IN is floating or grounded, then about 0.5 mA will leak from the Vs pin into the IC and about 3mA will leak from the OUT pin into the IC. From this leakage, about 50 uA will flow out of the IN pin and the rest will flow to ground. This does not affect long term reliability of the IC, but may influence circuit design. See Reverse Input Voltage Protection With IQ Reduction for details on how to avoid this leakage current.

3. OFF Pin

The OFF pin is a logic level input pin that is used to control the gate drive to the external MOSFET. The maximum operating voltage on this pin is 5.5 V. When the OFF pin is high, the MOSFET is turned off (independent of the sensed IN and OUT voltages). In this mode, load current will flow through the body diode of the MOSFET. The voltage difference between the IN pin and OUT pins will be approximately 700 mV if the MOSFET is operating normally through the body diode. The OFF pin has an internal pulldown of 5 µA (typical). If the OFF function is not required the pin may be left open or connected to ground.

4. Application Information

Systems that require high availability often use multiple redundant power supplies connected in parallel to increase reliability. Schottky OR-ing diodes are often used to connect these redundant supplies to the common point of the load. The disadvantage of using OR-ing diodes is the forward voltage drop, which reduces the available voltage and associated power losses as the load current increases. Replacing OR-ing diodes with N-channel MOSFETs requires a slightly increased level of complexity, but reduces or eliminates the need for diode heat sinks or large thermally conductive copper areas in board layouts for high power applications. The LM5050Q1MK-1/NOPB is a positive voltage (i.e. high side) OR-ing controller that will drive an external N-channel MOSFET in place of the OR-ing diode. The voltage on the MOSFET SOURCE and DRAIN pins is determined by The LM5050-1 is on the IN and OUT pins, while the GATE pin drives the MOSFET to control its operation based on the monitored source-drain voltage. The resulting behavior is that of an ideal rectifier, where the source and drain pins of the MOSFET act as the anode and cathode pins of the diode, respectively