LM5050-1, LM5050-1-Q1

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SNVS629E – MAY 2011 – REVISED DECEMBER 2015

Feature Description (continued)

If the MOSFET current reverses, possibly due to failure of the input supply, such that the voltage across the

quickly discharge the MOSFET gate through a strong GATE to IN pin discharge transistor.

If the input supply fails abruptly, as would occur if the supply was shorted directly to ground, a reverse current

will temporarily flow through the MOSFET until the gate can be fully discharged. This reverse current is sourced

from the load capacitance and from the parallel connected supplies. The LM5050-1 responds to a voltage

reversal condition typically within 25 ns. The actual 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.

7.3.2 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.

separate supply. This separate VS supply must be from 5 V and 75 V. See Figure 27.

7.3.3 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.

7.4 Device Functional Modes

7.4.1 ON/OFF Control Mode

is still available through the body diode of the MOSFET.

7.4.2 External Power Supply Mode

can be as low as 1 V, as shown in Figure 27.

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