LT1640H_15 Datasheet, PDF (7/16 Pages) Linear Technology – Negative Voltage Hot Swap Controller

LT1640L/LT1640H
APPLICATIONS INFORMATION
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 LT1640 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.
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_EE pin of the LT1640). R1 provides current fault
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:
I_INRUSH = (45µA • C_L)/C2
where C_L is the total load capacitance, C3 + C4 + module
input capacitance.
(SHORT PIN)
GND
GND
UV = 37V
OV = 71V
R4
562k
1%
R5
9.09k
1%
R6
10k
1%
3
UV
2
OV
V_EE
4
8
V_DD
LT1640H
SENSE
5
GATE
6
PWRGD
C3 +
0.1µF
100V
1
C4
100µF
100V
DRAIN
7
*
R1
0.02Ω
3 _5% 4
– 48V
1
2
* DIODES INC. SMAT70A
2× 1N4148
C1
150nF
25V
R2 _R3
10Ω _18k C2
5% _5% 3.3nF
100V
Q1
IRF530
Figure 6a. Inrush Control Circuitry
1640 F06a
VICOR
VI-J3D-CY
V_IN+
V_OUT+
5V
GATE IN
+ C5
100µF
16V
V_IN–
V_OUT–
1640lhfb
7