LTC4219 LINER [Linear Technology], LTC4219 Datasheet - Page 10

• Manufacturer Part Number: LTC4219
• Description: 5A Integrated Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTC4219
The typical LTC4219 application is in a high availability
system that uses a positive voltage supply to distribute
power to individual cards. A complete application circuit
is shown in Figure 1. External component selection is
discussed in detail in the following sections.
Turn-On Sequence
Several conditions must be present before the internal
pass MOSFET can be turned on. First the supply V
exceed its undervoltage lockout level. Next the internally
generated supply INTV
voltage threshold. This generates a 25μs power-on-reset
pulse which clears the fault register and initializes internal
latches. Finally, the enable inputs EN1 and EN2 both must
be below the 1.15V threshold. All of these conditions must
be satisfi ed for the duration of 100ms to ensure that any
contact bounce during the insertion has ended.
The MOSFET is turned on by charging up the GATE with
a charge pump generated current source whose value is
adjusted by shunting a portion of the pull-up current to
ground. The charging current is controlled by the INRUSH
circuit that maintains a constant slope of GATE voltage
10
12V
CC
must cross its 2.65V under-
C
0.1μF
T
Figure 1. 2A, 12V Card Resident Application
12V
C1
0.1μF
R1
10k
DD
V
EN1
EN2
FLT
TIMER
INTV
must
DD
CC
LTC4219DHC-12
GND
versus time (Figure 2). The voltage at the GATE pin rises
with a slope of 0.3V/ms and the supply inrush current is
set at:
This gate slope is designed to charge up a 1000μF capaci-
tor to 12V in 40ms, with an inrush current of 300mA. This
allows the inrush current to stay under the current limit
threshold (1.5A) for capacitors less than 1000μF . Included
in the Typical Performance Characteristics section is a
graph of the Safe Operating Area for the MOSFET. It is
evident from this graph that the power dissipation at 12V,
300mA for 40ms is in the safe region.
V
I
DD
GATE
INRUSH
I
OUT
MON
I
SET
PG
+ 6.15
V
DD
= C
R
1k
R
20k
R
20k
GATE
SET
MON
C
0.1μF
L
GATE
+
• (0.3V/ms)
Figure 2. Supply Turn-On
C
330μF
L
12V
SLOPE = 0.3V/ms
R4
10k
ADC
V
12V
2A
OUT
4219 F01
t1
t2
4219 F02
GATE
OUT
4219f