LTC1642_15 Datasheet, PDF (14/16 Pages) Linear Technology – Hot Swap Controller

LTC1642
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_CC falls below the chip’s
2.5V internal undervoltage lockout threshold.
To disable the undervoltage monitor, tie FB to REF and
ground RESET.
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, 0.1µF
ensures an adequate phase margin, but the minimum
compensation increases if REF sources a substantial DC
current, as shown in Figure 14.
R2
Q1
V_IN
0.015Ω
FDS6630A
12V
2.5A
16
15
V_CC SENSE
R3
100Ω
4
ON
14
GATE
R4
LTC1642
330Ω
C2
0.047µF
7
FB
5
RESET
+
V_OUT
C_LOAD
R9
95.3k
1%
R8
12.4k
1%
D1
1N4705
18V
RST TMR GND
3
8
C1
0.33µF
1642 F12
ALL RESISTORS ±5% UNLESS NOTED.
FB COMPARATOR TRIPS AT V_OUT = 10.7V
Figure 12. Undervoltage Monitoring Circuitry
V_IN
20V/DIV
V_RSTTMR
1V/DIV
V_RESET
10V/DIV
t₁
t₂ t₃
t₄
t₅
250ms/DIV
1642 F09
Figure 13. Supply Monitor Waveforms
10.0
4.0
2.0
1.0
0.4
0.2
0.1
14
100µA
1mA
REFERENCE CURRENT
10mA
1642 F14
Figure 14. Minimum REF Compensation vs REF Current
1642fb