Datasheet

-5 0 5 10 15 20 25

-2

VOLTS (V)

TIME (s)

INPUT B- Shorted

INPUT A-

INPUT B-

GATE Q1

GATE Q2

X.XXX V

2.000 A

PRODIGIT 3314

³$´

48.0V @ 5A

³%´

48.5V @ 3A

Inductive Kick-Back Protection

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Figure 1. Typical Board Connections

4 Inductive Kick-Back Protection

Diode D1 and capacitor C3 serve as inductive kick-back protection to limit negative transient voltage

spikes generated on the input when the INPUT A supply voltage is abruptly taken to zero volts. Diode D2

and capacitor C4 serve the same protective function on the INPUT B supply voltage.

Diode D4 and capacitors C5/C6 serve as inductive kick-back protection to limit positive transient voltage

spikes generated on the output when an input supply voltage is abruptly taken to zero volts.

5 OR-ing Transfer

An example of OR-ing transfer is shown in Figure 2. In this example one 48.5V supply (INPUT B) is

powering a 2A load at the output, while a 48.0V supply (INPUT A) is connected, but is idle. The OR-ing

transfer begins when the 48.5V supply is shorted (INPUT B- is shorted to INPUT B+). This short causes

reverse current through the MOSFET (Q2) and creates the required voltage (V

SD(REV)

+ ΔV

SD(REV)

) on the

LM5051 INN pin (U2) that will immediately cause the discharge the gate of the Q2 MOSFET.

Figure 2. Forward and Reverse Waveforms

AN-2148 LM5051MAEVAL Evaluation Board SNVA483B–October 2011–Revised May 2013

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