lt1963aes8-trpbf Linear Technology Corporation, lt1963aes8-trpbf Datasheet - Page 17

• Manufacturer Part Number: lt1963aes8-trpbf
• Description: 1.5a, Low Noise, Fast Transient Response Ldo Regulators
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
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 1.21V reference when the output is forced to 20V.
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 13V difference between OUT and ADJ
pins divided by the 5mA maximum current into the ADJ pin
yields a minimum top resistor value of 2.6k.
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 flow back into the output will follow
the curve shown in Figure 12.
When the IN pin of the LT1963A 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
U
U
W
U
input of the device 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.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Figure 12. Reverse Output Current
0
LT1963A-2.5
LT1963A-1.5
LT1963A-1.8
V
V
V
OUT
OUT
OUT
1
V
OUT
= V
= V
= V
2
LT1963A
FB
= V
FB
FB
OUTPUT VOLTAGE (V)
3
ADJ
4
LT1963A Series
5
6
T
V
CURRENT FLOWS
INTO OUTPUT PIN
J
IN
= 25°C
= 0V
7
LT1963A-3.3
V
OUT
8
= V
9
FB
1963 F12
10
17
1963afb