ltc1642a Linear Technology Corporation, ltc1642a Datasheet - Page 14

• Manufacturer Part Number: ltc1642a
• Description: Hot Swap Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
The undervoltage monitor behaves differently if FB is
above its threshold when the GATE begins ramping:
RESET goes high as soon as the GATE ramp begins.
RESET goes low immediately if V
2.5V internal undervoltage lockout threshold.
To disable the undervoltage monitor, tie FB to REF and
ground RESET.
LTC1642A
14
2.5A
12V
V
ALL RESISTORS ±5% UNLESS NOTED.
FB COMPARATOR TRIPS AT V
IN
0.33µF
Figure 12. Undervoltage Monitoring Circuitry
4
C1
ON
RST TMR
V
CC
LTC1642A
16
0.015Ω
3
R2
SENSE
RESET
GND
U
GATE
15
8
FB
14
7
5
FDS6630A
OUT
U
Q1
= 10.7V
R3
100Ω
R4
330Ω
C2
0.047µF
CC
Figure 14. Minimum REF Compensation vs REF Current
W
falls below the chip’s
R9
95.3k
1%
R8
12.4k
1%
10.0
+
4.0
2.0
1.0
0.4
0.2
0.1
100µA
1642a F12
D1
1N4705
18V
C
U
V
LOAD
OUT
REFERENCE CURRENT
1mA
Reference
The LTC1642A’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, 0.1µF
ensures an adequate phase margin, but the minimum
compensation increases if REF sources a substantial DC
current, as shown in Figure 14.
V
20V/DIV
10V/DIV
RSTTMR
1V/DIV
V
RESET
V
IN
1642a F14
Figure 13. Supply Monitor Waveforms
10mA
t
1
t
2
t
3
250ms/DIV
t
4
t
5
1642a F13
1642af