LT3579 datasheet(23/40 Pages) LINER

23 / 40 page

LT3579/LT3579-1

35791f

APPLICATIONS INFORMATION

VIN

12V

VOUT2

100V

200mA

VOUT1

67V

100mA

10μH

4.7μF

6.8μF

4.7μF

6.8μF

100k

10μF

SW1 SW2

VIN

CLKOUT

GND

GATE

FAULT

SYNC

SHDN

LT3579

3579 F16

383k

6.5k

34k

470pF

2.2μF

27pF

86.6k

536k

VIN

Figure 16. High VOUT Charge Pump Topology

VIN

CIN

CSS

–VOUT

SW1

SW2

VIN

CLKOUT

GND

GATE

SHDN

FAULT

SYNC

LT3579

COUT

100k

RFB

3579 F15

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 LT3579. Since

the GATE pin pull-down current is linearly proportional to

the SS voltage, and the SS charge up time is relatively slow,

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

limited during a hot-plug event. To illustrate this, the circuit

in Figure 6 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

the result of hot-plugging this re-conﬁgured circuit. The

inductor current is well behaved and VOUT comes up once

VIN settles out.

Figure 15. Single Inductor Inverting Topology

Figure 14. VIN Hot-Plug Control. Inrush Current is Well Controlled

1s/DIV

VIN

5V/DIV

VOUT

10V/DIV

5A/DIV

1V/DIV

3579 F14

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