LTC1647 LINER [Linear Technology], LTC1647 Datasheet - Page 13

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

OPERATION
HOT CIRCUIT INSERTION
When circuit boards are inserted into or removed from
live backplanes, the supply bypass capacitors can draw
huge transient currents from the backplane power bus as
they charge. The transient current can cause permanent
damage to the connector pins as well as cause glitches
on the system supply, causing other boards in the system
to reset.
The LTC4211 is designed to turn a printed circuit board’s
supply voltages ON and OFF in a controlled manner, al-
lowing the circuit board to be safely inserted or removed
from a live backplane. The device provides a system
reset signal to indicate when board supply voltage drops
below a predetermined level, as well as a dual function
fault monitor.
OUTPUT VOLTAGE MONITOR
The LTC4211 uses a 1.236V bandgap reference, precision
voltage comparator and an external resistor divider to
monitor the output supply voltage as shown in Figure 1.
The operation of the supply monitor in normal mode is
illustrated in Figure 2. When the voltage at the FB pin
drops below its reset threshold (1.236V), the comparator
ON/RESET
GND
V
CC
CONNECTOR
BACKPLANE
(FEMALE)
CONNECTOR
PCB EDGE
(MALE)
LONG
SHORT
LONG
Figure 1. Supply Voltage Monitor Block Diagram
2
ON
LTC4211
TIMER
LOGIC
TIMER
3
C
TIMER
V
CC
8
R
COMP2 output goes high. After a glitch filter delay, RESET
is pulled low (Time Point 1). When the voltage at the FB
pin rises above its reset threshold (1.239V), COMP2’s
output goes low and a timing cycle starts (Time Point 4).
After a complete timing cycle, RESET is pulled high by
the external pull-up resistor. If the FB pin rises above the
reset threshold for less than a timing cycle, the RESET
output remains low (Time Points 2 to 3).
As shown in Figure 5, the LTC4211’s RESET pin is logic
low during any undervoltage lockout condition and during
the initial insertion of a PC board. Under normal opera-
tion, RESET goes to logic high at the end of the soft-start
cycle only after the FB pin voltage rises above its reset
threshold of 1.239V.
SENSE
REFERENCE
COMP2
SENSE
1.236V
Figure 2. Supply Monitor Waveforms in Normal Mode
7
TIMER
RESET
–
+
V
OUT
GATE
Q1
6
1
4
Q2
GND
RESET
V1
FB
V2
5
1
2
3
R1
R2
V1
R3
10k
4211 F01
V2
RESET
μP
4
POWER GOOD
+
DELAY
V
C
LTC4211
OUT
LOAD
1.236V
4211 F02
13
4211fb