LM5050-1, LM5050-1-Q1

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SNVS629E – MAY 2011 – REVISED DECEMBER 2015

7 Detailed Description

7.1 Overview

Blocking diodes are commonly placed in series with supply inputs for the purpose of ORing redundant power

sources and protecting against supply reversal. The LM5050 replaces diodes in these applications with an N-

MOSFET to reduce both the voltage drop and power loss associated with a passive solution. At low input

voltages, the improvement in forward voltage loss is readily appreciated where headroom is tight, as shown in

Figure 2. The LM5050 operates from 5 V to 75 V and it can withstand an absolute maximum of 100 V without

damage. A 12-V or 15-A ideal diode application is shown in Figure 24. Several external components are included

in addition to the MOSFET, Q1. Ideal diodes, like their non-ideal counterparts, exhibit a behavior known as

reverse recovery. In combination with parasitic or intentionally introduced inductances, reverse recovery spikes

may be generated by an ideal diode during an reverse current shutdown. D1, D2 and R1 protect against these

spikes which might otherwise exceed the LM5050 100-V survival rating. COUT also plays a role in absorbing

reverse recovery energy. Spikes and protection schemes are discussed in detail in the Short Circuit Failure of an

Input Supply section.

NOTE

The OFF pin may be used to active the GATE pull down circuit and turn off the pass

MOSFET, but it does not disconnect the load from the input because Q1’s body diode is

still present.

If Vs is powered while IN is floating or grounded, then about 0.5mA 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.

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Product Folder Links: LM5050-1 LM5050-1-Q1