LT3013MPFE Linear Technology, LT3013MPFE Datasheet - Page 17

• Manufacturer Part Number: LT3013MPFE
• Description: SP-LINREG, 80Vin, 250mA, LDO W/ PWRGD In TSSOP
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
In situations where the ADJ pin is connected to a resistor
divider that would pull the ADJ pin above its 7V clamp
voltage 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
1.24V 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
200
180
160
140
120
100
80
60
40
20
0
Figure 5. Reverse Output Current
0
T
V
V
CURRENT FLOWS
INTO OUTPUT PIN
J
IN
OUT
= 25°C
1
= 0V
= V
2
ADJ
OUTPUT VOLTAGE (V)
3
4
5
open-circuit. Current fl ow back into the output will follow
the curve shown in Figure 5. 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 LT3013 is forced below the OUT
pin or the OUT pin is pulled above the IN pin, input current
will typically drop to less than 2μA. This can happen if
the input of the LT3013 is connected to a discharged
(low voltage) battery and the output is held up by either
a backup battery or a second regulator circuit. The state
of the SHDN pin will have no effect on the reverse output
current when the output is pulled above the input.
6
(SEE ABOVE)
PIN CLAMP
7
ADJ
8
9
3013 F05
10
LT3013
17
3013fe