LTC1642C LINER [Linear Technology], LTC1642C Datasheet - Page 10

• Manufacturer Part Number: LTC1642C
• Description: Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

LTC1642
APPLICATIO S I FOR ATIO
Undervoltage Monitor
The LTC1642 will assert RESET if a monitored voltage falls
below a programmable minimum. When the monitored
voltage has exceeded its minimum for at least one system
timing cycle, RESET goes high. The monitoring circuitry
comprises an internal 1.23V bandgap reference, an inter-
nal precision voltage comparator and an external resistive
divider to monitor the output supply voltage. The circuit is
shown in Figure 12, and typical waveforms in Figure 13.
When the voltage at the FB pin rises above its reset
threshold (1.23V), the comparator output goes low and a
timing cycle starts (times 1 and 5). Following the cycle
RESET is pulled high.
At time 2 the voltage at FB drops below the comparator’s
threshold and RESET is pulled low. If the FB pin rises
above the reset threshold for less than a timing cycle the
RESET output will remain low (time 3 to time 4). The 15 A
pull-up current source to V
so the pin can be pulled above V
resistor without forcing current back into the supply.
Reference
The LTC1642’s internal voltage reference is buffered and
brought out to the REF pin. The buffer amplifier should be
compensated with a capacitor connected between REF
and ground. If no DC current is drawn from REF, 0.1 F
ensures an adequate phase margin, but the minimum
compensation increases if REF sources a substantial DC
current, as shown in Figure 14.
Uncommitted Comparator
The uncommitted comparator has an open drain output.
The comparator has 3mV of hysteresis: the output goes
high when the differential input voltage exceeds 1.5mV
and goes low when the differential input is less than
–1.5mV.
10
U
U
CC
on RESET has a series diode
CC
by an external pull-up
W
U
Figure 14. Minimum REF Compensation vs REF Current
2.5A
12V
V
ALL RESISTORS 5% UNLESS NOTED.
FB COMPARATOR TRIPS AT V
IN
Figure 12. Undervoltage Monitoring Circuitry
0.33 F
RST TMR
4
RESET
C1
Figure 13. Supply Monitor Waveforms
ON
V
10.0
RST TMR
4.0
2.0
1.0
0.4
0.2
0.1
OUT
V
100 A
CC
LTC1642
16
0.010
V1
3
R2
1
SENSE
GND
RESET
GATE
15
8
FB
REFERENCE CURRENT
14
7
5
OUT
2
FDR9410A
V2
Q1
= 10.7V
1mA
V1
R3
100
R4
330
3
C2
0.047 F
4
V2
5
V1
R7
95.3k
1%
R6
12.4k
1%
+
1642 F14
1642 F13
10mA
C
LOAD
1642 F12
V
OUT