LTC4211 LINER [Linear Technology], LTC4211 Datasheet - Page 20

• Manufacturer Part Number: LTC4211
• Description: Hot Swap Controller with Multifunction Current Control
• Manufacturer: LINER [Linear Technology]

OPERATIO
LTC4211
start-up sequence where the LTC4211 is powered up into
a load overcurrent condition. Note that the circuit breaker
trips at Time Point B and is reset at Time Point 9A.
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 20 s. During normal operation, the FILTER
output pin is held low as an internal 10 A 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 2 A pull-up
current source is connected to the FILTER pin by transis-
tor M5, thereby charging C
capacitor accumulates, the voltage across C
20
V
CC
– V
FILTER
TIMER
RESET
U
FAULT
SENSE
GATE
V
V
OUT
CC
Figure 10. Power-Up in Overcurrent, Slow Comparator Trips the Circuit Breaker
1 2
FILTER
ON
. As the charge on the
V
FB
< V
REF
3 4 5
FAST COMPARATOR ARMED
FILTER
LOAD CURRENT
V
REGULATING
SENSE
6
= 50mV
GATE
V
OUT
increases. Once the FILTER pin voltage increases to 1.236V,
the electronic circuit breaker trips and the LTC4211’s
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 10 A 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 = 638 s. As a design aid, SLOW COMP’s delay time
(t
from 100pF to 1000pF is illustrated in Table 2.
SLOW COMP
t
SLOWCOMP
7 8
SLOW COMPARATOR ARMED
t
FAULTSC
>50mV
2 A
) versus C
CIRCUIT BREAKER TRIPS
B
FPD
V
REF
FILTER
10 A
1 236
.
ON
FILTER
= 1000pF, SLOW COMP’s response
t
V
9
RESET
•
9A
CIRCUIT BREAKER RESET
C
for standard values of C
FILTER
2
A
1
ON
20
4211 F10
s
FILTER
4211f
(7)