Datasheet

LTC4211
13
4211fb
OPERATION
+
SENSE
R
SENSE
R2
R1
R3
10k
7
V
CC
V
OUT
8
GATELTC4211
6
2
FB
Q2
GND
ON
4211 F01
1RESET
5
C
TIMER
3
TIMER
4
C
LOAD
Q1
LOGIC
TIMER
1.236V
REFERENCE
COMP2
μP
RESET
SHORT
LONG
V
CC
ON/RESET
GND
LONG
PCB EDGE
CONNECTOR
(MALE)
BACKPLANE
CONNECTOR
(FEMALE)
+
–
V
OUT
TIMER
RESET
V2 V2V1V1
1.236V
POWER GOOD
DELAY
1234
4211 F02
Figure 1. Supply Voltage Monitor Block Diagram
Figure 2. Supply Monitor Waveforms in Normal Mode
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
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.