LTC1647 LINER [Linear Technology], LTC1647 Datasheet - Page 17

• Manufacturer Part Number: LTC1647
• Description: Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

OPERATION
SOFT-START WITH CURRENT LIMITING
During the second timing cycle, the inrush current was
described by Equation 4. Note that there is a one-to-one
correspondence in the inrush current to C
current is large enough to cause a voltage drop greater
than 50mV across the sense resistor, an internal servo
loop controls the operation of the 10μA current source at
the GATE pin to regulate the load current to:
For example, the inrush current is limited to 5A when
R
SENSE
I
LIMIT(SOFTSTART)
= 0.01Ω.
TIMER
RESET
I
GATE
V
LOAD
V
OUT
ON
CC
1 2
=
Figure 7. Normal Power-Up Sequence (with Current Limiting in Second Timing Cycle)
CHECK FOR GATE < 0.2V
R
FIRST TIMING CYCLE
50mV
SENSE
PLUG-IN CYCLE
2μA
V
REF
3 4 5
REGULATING AT 50mV/R
CHECK FOR FILTER LOW (<V
CHECK FOR FAULT HIGH (>V
LOAD
FAST COMPARATOR ARMED
LOAD CURRENT IS
SECOND TIMING CYCLE
5A
SOFT-START CYCLE
10μA
. If the inrush
6
POWER GOOD
V
FB
2μA
> V
SENSE
REF
(6)
REF
REF
SLOW COMPARATOR ARMED
7 8
+ 50mV)
– 80mV)
In this fashion, the inrush current is controlled and C
is charged up slowly during the soft-start cycle.
The timing diagram in Figure 7 illustrates the operation
of the LTC4211 in a normal power-up sequence with lim-
ited inrush current as described by Equation 6. At Time
Point 5, the GATE pin voltage begins to ramp and the power
MOSFET starts to charge C
current causes a 50mV voltage drop across R
the internal servo loop engages, limiting the inrush cur-
rent to a fixed level. At Time Point 6, the GATE pin voltage
continues to ramp as C
final value. The charging current reduces, and the internal
servo loop disengages. At the end of the soft-start cycle
(Time Point 7), RESET is high and SLOW COMP is armed.
GATE
V
OUT
POWER BAD
V
FB
< V
REF
ON GOES LOW
9
10
RESET PULLED LOW DUE TO POWER BAD
LOAD
200μA
LOAD
charges until V
. At Time Point 5A, the inrush
4211 F07
LTC4211
OUT
reaches its
SENSE
17
LOAD
4211fb
and