LTC1642 Linear Technology, LTC1642 Datasheet - Page 9

• Manufacturer Part Number: LTC1642
• Description: Hot Swap Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
goes low at time 7, and GATE begins charging at time 8,
one RST TMR cycle after FAULT goes high.
Figure 10 shows typical waveforms when the OV divider is
driven from the N-channel’s low side. Because the voltage
driving the divider collapses after the OV comparator trips,
FAULT stays high and CRWBR stays near ground, which
prevents the pin from triggering an SCR. The GATE voltage
begins ramping up after a RST TMR timing cycle.
Automatic Restart
If there is an overvoltage, and the resistor divider feeding
OV is connected to the output of the N-channel pass
transistor, the LTC1642 will automatically restart even if
FAULT is not tied to ON. If the divider is connected to the
input side, the LTC1642 will restart itself only if FAULT is
tied to ON, and only after the overvoltage clears.
Figure 10. Overvoltage Timing (Low Side)
RST TMR
V
OV
GATE
V
CRWBR
FAULT
CC
OUT
1
U
2
3
U
4
5
6 7
W
1642 F10
0V
1.23V
0V
0.41V
1.23V
0V
U
The OV and FB Comparators
The propagation delay through the OV and FB compara-
tors on low to high transitions depends strongly on the
differential input voltage. The relationship is shown in
Figure 11. The minimum propagation delay for large
overdrives is about 20 s. In addition the comparators
have 3mV of hysteresis.
Internal Voltage Clamp Protection
The LTC1642 includes a shunt regulator to protect itself
from V
turns on when V
chip’s circuitry to 15V. When it is on the chip functions
normally with one exception: if the charge pump is on, the
GATE voltage is usually near ground but this is not
guaranteed. Use the OV pin to ensure that GATE is grounded.
The pull-up voltage on the RESET and FAULT pins follows
V
is on the pull-up voltage is 14.4V.
CC
until the shunt regulator turns on. When the regulator
CC
Figure 11. OV Comparator Propagation Delay vs
Overdrive Voltage
and SENSE pin voltages up to 33V. The regulator
70
60
50
40
30
20
10
0
0
CC
exceeds 16.5V and limits most of the
40
OV OVERDRIVE (mV)
80
120
160
200
LTC1642
1642 F11
240
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