lt3579iufd-trpbf Linear Technology Corporation, lt3579iufd-trpbf Datasheet - Page 23

• Manufacturer Part Number: lt3579iufd-trpbf
• Description: Lt3579/lt3579-1 6a Boost/inverting Dc/dc Converter With Fault Protection Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
HOT PLUG
The high inrush current associated with hot-plugging V
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
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 V
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-confi gured 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-confi gured circuit. The
inductor current is well behaved and V
V
Figure 14. V
IN
settles out.
IN
hot-plugs or ramps up sharply.
10V/DIV
IN
5V/DIV
5A/DIV
1V/DIV
V
Hot-Plug Control. Inrush Current is Well Controlled
OUT
V
SS
IN
I
L
1s/DIV
IN
, with the gate of the
OUT
comes up once
3579 F14
IN
12V
V
V
IN
IN
10μF
C
IN
Figure 15. Single Inductor Inverting Topology
Figure 16. High V
100k
536k
86.6k
100k
R
10μH
T
L1
V
FAULT
SHDN
RT
SYNC
IN
V
SHDN
FAULT
RT
SW1 SW2
SYNC
IN
LT3579
SW1
GND
LT3579
CLKOUT
GND
D1
LT3579/LT3579-1
OUT
GATE
SW2
CLKOUT
SS
FB
V
4.7μF
4.7μF
C
Charge Pump Topology
GATE
SS
2.2μF
C1
V
FB
C
C
6.8μF
383k
SS
D2
27pF
6.5k
D3
C
F
4.7μF
4.7μF
34k
470pF
R
3579 F16
R
V
C
C
FB
3579 F15
IN
C
23
6.8μF
–V
V
100V
200mA
V
67V
100mA
C
35791f
OUT2
OUT1
OUT
OUT