Datasheet

LT3581
21
3581fa
For more information www.linear.com/LT3581
V
OUT
10V/DIV
SS
1V/DIV
I
L
5A/DIV
V
IN
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 V
IN
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 V
IN
, 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
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 V
IN
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 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
the results of hot-plugging this re-configured circuit. Notice
how the inductor current is well behaved.