Datasheet

LT4254
9
4254fb
TEST CIRCUIT
TI I G DIAGRA S
WUW
UV
4254 F02
GATE
V
OUT
+2V
t
PLHUV
4V
V
OUT
+2V
t
PHLUV
3.6V
FB
4254 F03
PWRGD
1V
t
PLHFB
4.45V
1V
t
PHLFB
4V
V
CC
– SENSE
4254 F04
GATE
V
CC
t
PHLSENSE
50mV
Figure 2. UV to GATE Timing Figure 3. V
OUT
to PWRGD Timing
Figure 4. SENSE to GATE Timing
Figure 1
V
CC
SENSE
GATE
TIMER
RETRY
PWRGD
OPEN
FB
OV
UV
24V
GND
3V
3V
4254 TC
100pF
+
–
+
–
+
–
APPLICATIO S I FOR ATIO
WUU
U
Hot Circuit Insertion
When circuit boards are inserted into a live backplane, the
supply bypass capacitors on the boards draw high peak
currents from the backplane power bus as they charge.
The transient currents can permanently damage the con-
nector pins and glitch the system supply, causing other
boards in the system to reset.
The LT4254 is designed to turn on a board’s supply
voltage in a controlled manner, allowing the board to be
safely inserted or removed from a live backplane. The
device also provides undervoltage and overvoltage as well
as overcurrent protection while a power good output
signal indicates when the output supply voltage is ready
with a high output.
Power-Up Sequence
An external N-channel MOSFET pass transistor (Q1) is
placed in the power path to control the power up of the
supply voltage (Figure 5). Resistor R5 provides current
detection and capacitor C1 controls the GATE slew rate.