LTC1647 LINER [Linear Technology], LTC1647 Datasheet - Page 21

• Manufacturer Part Number: LTC1647
• Description: Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

OPERATION
ADJUSTING SLOW COMP’S RESPONSE TIME
The response time of SLOW COMP is adjusted using a
capacitor connected from the LTC4211’s FILTER pin to
ground. If this pin is left unused, SLOW COMP’s delay
defaults to 20μs. During normal operation, the FILTER
output pin is held low as an internal 10μA pull-down
current source is connected to this pin by transistor M4.
This pull-down current source is turned off when an
overcurrent load condition is detected by SLOW COMP.
During an overcurrent condition, the internal 2μA pull-
up current source is connected to the FILTER pin by
transistor M5, thereby charging C
on the capacitor accumulates, the voltage across C
increases. Once the FILTER pin voltage increases to 1.236V,
the electronic circuit breaker trips and the LTC4211’s
V
CC
– V
FILTER
TIMER
RESET
FAULT
SENSE
GATE
V
V
OUT
CC
Figure 10. Power-Up in Overcurrent, Slow Comparator Trips the Circuit Breaker
1 2
ON
FILTER
V
FB
< V
. As the charge
REF
3 4 5
FAST COMPARATOR ARMED
FILTER
LOAD CURRENT
V
REGULATING
SENSE
6
= 50mV
GATE
V
GATE pin is switched quickly to ground by transistor M3.
After the circuit breaker is tripped, M5 is turned OFF, M4
is turned ON and the 10μA pull-down current then holds
the FILTER pin voltage low.
The SLOW COMP response time from an overcurrent fault
condition to when the circuit breaker trips (GATE OFF) is
given by Equation 7:
For example, if C
time = 638μs. As a design aid, SLOW COMP’s delay time
(t
from 100pF to 1000pF is illustrated in Table 2.
OUT
SLOW COMP
t
SLOWCOMP
7 8
SLOW COMPARATOR ARMED
t
FAULTSC
>50mV
2μA
) versus C
CIRCUIT BREAKER TRIPS
B
= 1.236V •
FILTER
FPD
V
REF
10μA
= 1000pF, SLOW COMP’s response
FILTER
ON
t
9
RESET
C
9A
for standard values of C
CIRCUIT BREAKER RESET
FILTER
2µA
1
+ 20µs
ON
LTC4211
4211 F10
21
FILTER
4211fb
(7)