LT1640AH LINER [Linear Technology], LT1640AH Datasheet - Page 7

• Manufacturer Part Number: LT1640AH
• Description: Negative Voltage Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Hot Circuit Insertion
When circuit boards are inserted into a live – 48V backplane,
the bypass capacitors at the input of the board’s power
module or switching power supply can draw huge tran-
sient currents as they charge up. The transient currents
can cause permanent damage to the board’s components
and cause glitches on the system power supply.
The LT1640A 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 chip
also provides undervoltage, overvoltage and overcurrent
protection while keeping the power module off until its
input voltage is stable and within tolerance.
UV = 37V
OV = 71V
* DIODES INC. SMAT70A
– 48V
GND
*
GND
9.09k
562k
10k
1%
1%
1%
R4
R5
R6
U
(SHORT PIN)
3
2
U
UV
OV
3
V
EE
4
1
0.02
5%
R1
W
SENSE
2
4
5
C1
150nF
25V
LT1640AH
Figure 6a. Inrush Control Circuitry
GATE
V
DD
U
8
6
IRF530
Q1
R2
10
5%
18k
5%
R3
3.3nF
100V
C2
PWRGD
DRAIN
Power Supply Ramping
The input to the power module on a board is controlled by
placing an external N-channel pass transistor (Q1) in the
power path (Figure 6a, all waveforms are with respect to
the V
detection and R2 prevents high frequency oscillations.
Resistors R4, R5 and R6 provide undervoltage and over-
voltage sensing. By ramping the gate of Q1 up at a slow
rate, the surge current charging load capacitors C3 and C4
can be limited to a safe value when the board makes
connection.
Resistor R3 and capacitor C2 act as a feedback network to
accurately control the inrush current. The inrush current
can be calculated with the following equation:
where C
module input capacitance.
7
I
INRUSH
EE
1
L
pin of the LT1640A). R1 provides current fault
is the total load capacitance equal to C3 + C4 +
C3
0.1 F
100V
= (45 A • C
+
1640A F06a
C4
100 F
100V
LT1640AL/LT1640AH
L
)/C2
V
GATE IN
V
IN
IN
+
–
VI-J3D-CY
VICOR
V
V
OUT
OUT
+
–
+
C5
100 F
16V
5V
7