LT3581 datasheet(21/36 Pages) LINER

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LT3581

3581f

VOUT

10V/DIV

1V/DIV

5A/DIV

VIN

5V/DIV

3581 F14

1s/DIV

applicaTions inForMaTion

Figure 14. Inrush Current Is Well Controlled in Spite Of Hot-

Plugging the Re-configured Boost Converter in Figure 18

HOT-PLUG

The high inrush current associated with hot-plugging VIN

can be largely rejected with the use of an external PMOS. A

simple hot-plug controller can be designed by connecting

an external PMOS in series with VIN, with the gate of the

PMOS being driven by the GATE pin of the LT3581. Since

the GATE pin pull-down current is linearly proportional to

theSSvoltage,andtheSSchargeuptimeisrelativelyslow,

the GATE pin pull-down current will increase gradually,

thereby turning on the external PMOS slowly. Controlled

in this manner, the PMOS acts as an input current limiter

when VIN hot-plugs or ramps up sharply.

Likewise, when the PMOS is connected in series with the

output, inrush currents into the output capacitor can be

limitedduringahot-plugevent.Toillustratethis,thecircuit

in Figure 18 was re-configured by adding a large 1500µF

capacitor to the output. An 18Ω resistive load was used

and a 2.2µF capacitor was placed on SS. Figure 14 shows

theresultsofhot-pluggingthisre-configuredcircuit.Notice

how the inductor current is well behaved.

LT3581 Datasheet(PDF) 21 Page - Linear Technology