LT4256-1 LINER [Linear Technology], LT4256-1 Datasheet - Page 8

• Manufacturer Part Number: LT4256-1
• Description: Positive High Voltage Hot Swap Controllers
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT4256-1/LT4256-2
TEST CIRCUIT
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 LT4256-1/LT4256-2 are 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
TI I G DIAGRA S
8
W U
GATE
UV
4V
Figure 2. UV to GATE Timing
2V
U
t
PLHUV
U
W
V
CC
W
– SENSE
GATE
3.6V
Figure 4. SENSE to GATE Timing
4256 F02
48k
2V
U
t
PHLUV
55mV
V
CC
PWRGD
FB
UV
t
PHLSENSE
Figure 1
GND
SENSE
TIMER
GATE
device also provides undervoltage 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.
Resistor R7 compensates the current control loop while
R6 prevents high frequency oscillations in Q1.
V
CC
4256 F01
PWRGD
48V
FB
+ –
Figure 3. V
100pF
4V
4256 F04
1V
t
PLHFB
OUT
to PWRGD Timing
3.65V
4256 F03
1V
t
PHLFB
425612f