LTC1642IGN Ver la hoja de datos (PDF) - Linear Technology
Número de pieza
componentes Descripción
Fabricante
LTC1642IGN Datasheet PDF : 16 Pages
| |||
LTC1642
APPLICATIO S I FOR ATIO
Automatic Restart After the Circuit Breaker Opens
The LTC1642 will automatically attempt to restart itself
after the circuit breaker opens if the FAULT output is tied
to the ON pin. The circuit is shown in Figure 5. Diode D1
blocks the weak FAULT pull-up current source from unbal-
ancing the R6-R5 divider.
During a continuous current limit such as a load short,
Q1’s duty cycle is equal to the circuit breaker timer period,
divided by the sum of the circuit breaker and system timer
periods:
Short - Circuit Duty Cycle = C4
C4 + 10 • C1
The duty cycle is 9% for the Figure 5 circuit. Waveforms
during a load short are shown in Figure 6.
Undervoltage Lockout
An internal undervoltage lockout circuit holds the charge
pump off until VCC exceeds 2.73V. If VCC falls below 2.5V,
it turns off the charge pump and clears overvoltage and
current limit faults.
For higher lockout thresholds tie the ON pin to a resistor
divider driven from VCC, as shown in Figure 7. This
circuit keeps the charge pump off until VCC exceeds
(1+R6/R5) • 1.34V, and also turns it off if VCC falls below
(1+R6/R5) • 1.22V.
VIN
12V
2.5A
R6
464k
1%
R2
0.015Ω
Q1
FDS6630A
16
VCC
4
ON
15
SENSE
14
GATE
+
R3
100Ω
VOUT
CLOAD
6
FAULT
R4
330Ω
D2
1N4705
D1
LTC1642
18V
1N4148
R5
60.4k
1%
2
BRK TMR
R10
30k
RST TMR GND
C2
0.047µF
C4
0.33µF
3
8
C1
0.33µF
ALL RESISTORS ±5% UNLESS NOTED
1642 F05
Figure 5. Automatic Restart Circuit
VGATE
20V/DIV
VOUT
10V/DIV
VBRKTMR
1V/DIV
VRSTTMR
1V/DIV
40ms/DIV
1642 F06
Figure 6. Automatic Retry Following a Load Short
VIN
12V
2.5A
UNDERVOLTAGE
LOCKOUT
THRESHOLD = 10.7V
R2
Q1
R6
464k
1%
0.015Ω
FDS6630A
16
VCC
15
SENSE
+
R3
100Ω
VOUT
CLOAD
LTC1642
4
ON
14
GATE
R5
60.4k
1%
RST TMR GND
3
8
C1
0.33µF
R4
330Ω
D1
1N4705
18V
C2
0.047µF
1642 F07
ALL RESISTORS ±5% UNLESS NOTED
Figure 7. Setting a Higher Undervoltage Lockout
1642fb
11
Share Link: 