6
LTC1643AL
LTC1643AL-1/LTC1643AH
1643afb
TYPICAL PERFORMANCE CHARACTERISTICS
UW
V
EE
Current Foldback
vs Temperature
I
SINK
(mA)
0
V
OL
(mV)
6
10
1643A G27
24 8
800
700
600
500
400
300
200
100
0
FAULT
PWRGD
V
OL
vs I
SINK
(25°C)
TIMER (Pin 4): Analog Current Fault Inhibit Timing Input.
Connect a capacitor from TIMER to GND. With the chip
turned off (ON = GND or ON = High) or the internal circuit
breaker tripped (FAULT = GND), the TIMER pin is internally
held at GND. When the chip is turned on, a 22µA pull-up
current source is connected to TIMER. Current limit faults
will be ignored until the voltage at the TIMER pin rises to
within 0.9V of 12V
IN
.
ON/ON (Pin 5): Digital Input.The LTC1643AL/LTC1643AL-1
have an active low enable, ON, and the LTC1643AH has an
active high enable, ON. When the ON pin is pulled high or
PIN FUNCTIONS
UUU
12V
IN
(Pin 1): 12V Supply Input. It powers all the chip’s
internal circuitry. A 0.5Ω switch is connected between
12V
IN
and 12V
OUT
with a foldback current limit. An under-
voltage lockout circuit prevents the switches from turning
on while the 12V
IN
pin voltage is less than 9.5V typically.
V
EEIN
(Pin 2): –12V Supply Input. A 1.2Ω switch is
connected between V
EEIN
and V
EEOUT
with a foldback
current limit.
3V
OUT
(Pin 3): Analog Input. Used to monitor the 3.3V
output supply voltage. The PWRGD signal cannot go low
until the 3V
OUT
pin exceeds 2.9V typically.
TEMPERATURE (°C)
70
60
50
40
30
20
10
0
1643A G24
FOLDBACK CURRENT LIMIT VOLTAGE (mV)
–50 25 75
–25 0
50 100 125
3V
OUT
= 3.3V
3V
OUT
= 0V
3V
IN
Foldback Current Limit
Voltage vs Temperature
TEMPERATURE (°C)
–50
UNDERVOLTAGE LOCKOUT (V)
2.454
2.452
2.450
2.448
2.446
2.444
2.442
25 75
1643A G21
–25 0
50 100 125
3V
IN
Undervoltage Lockout
vs Temperature
TEMPERATURE (°C)
70
60
50
40
30
20
10
0
1643A G23
FOLDBACK CURRENT LIMIT VOLTAGE (mV)
–50 25 75
–25 0
50 100 125
5V
OUT
= 5V
5V
OUT
= 0V
5V
IN
Foldback Current Limit
Voltage vs Temperature
12V
Current Foldback
vs Temperature
TEMPERATURE (°C)
–50
CURRENT FOLDBACK (mA)
1200
1000
800
600
400
200
0
25 75
1643A G26
–25 0
50 100
12V
OUT
= 12V
12V
OUT
= 0V
TEMPERATURE (°C)
–50
CURRENT FOLDBACK (mA)
600
500
400
300
200
100
0
25 75
1643A G25
–25 0
50 100
V
EEOUT
= –12V
V
EEOUT
= 0V
