Datasheet

LT3014B
10
3014bfa
left open circuit or grounded, the ADJ pin will act like an
open circuit when pulled below ground, and like a large
resistor (typically 100k) in series with a diode when pulled
above ground. If the input is powered by a voltage source,
pulling the ADJ pin below the reference voltage will cause
the device to current limit. This will cause the output to go
to an unregulated high voltage. Pulling the ADJ pin above
the reference voltage will turn off all output current.
In situations where the ADJ pin is connected to a resistor
divider that would pull the ADJ pin above its 7V clamp volt-
age if the output is pulled high, the ADJ pin input current
must be limited to less than 5mA. For example, a resistor
divider is used to provide a regulated 1.5V output from the
1.22V reference when the output is forced to 60V. The top
resistor of the resistor divider must be chosen to limit the
current into the ADJ pin to less than 5mA when the ADJ
pin is at 7V. The 53V difference between the OUT and ADJ
pins divided by the 5mA maximum current into the ADJ
pin yields a minimum top resistor value of 10.6k.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled
to ground, pulled to some intermediate voltage, or is left
open circuit. Current fl ow back into the output will follow
the curve shown in Figure 4. The rise in reverse output
current above 7V occurs from the breakdown of the 7V
clamp on the ADJ pin. With a resistor divider on the
regulator output, this current will be reduced depending
on the size of the resistor divider.
When the IN pin of the LT3014B is forced below the OUT
pin or the OUT pin is pulled above the IN pin, input cur-
rent will typically drop to less than 2μA. This can happen
if the input of the LT3014B is connected to a discharged
(low voltage) battery and the output is held up by either
a backup battery or a second regulator circuit.
APPLICATIONS INFORMATION
Figure 4. Reverse Output Current
OUTPUT VOLTAGE (V)
0
REVERSE OUTPUT CURRENT (μA)
50
45
40
30
35
25
20
15
10
5
0
8
3014B F04
21357946 10
T
J
= 25°C
V
IN
= 0V
V
OUT
= V
ADJ
CURRENT FLOWS
INTO OUTPUT PIN
ADJ PIN
ESD CLAMP
LT3014B Automotive Application
LT3014B Telecom Application
+
ADJ
OUTIN
LT3014B
GND
1μF
1μF
V
IN
12V
(LATER 42V)
LOAD: CLOCK,
SECURITY SYSTEM
ETC
+
–
ADJ
OUTIN
LT3014B
GND
1μF
1μF
V
IN
48V
(72V TRANSIENT)
LOAD:
SYSTEM MONITOR
ETC
NO PROTECTION
DIODE NEEDED!
NO PROTECTION
DIODE NEEDED!
3014B TA05
BACKUP
BATTERY
R1
R2
R1
R2
TYPICAL APPLICATIONS