IC LDO REG W/SHTDWN ADJ 8-MSOP

LT1521CMS8

Manufacturer Part NumberLT1521CMS8
DescriptionIC LDO REG W/SHTDWN ADJ 8-MSOP
ManufacturerLinear Technology
LT1521CMS8 datasheet
 


Specifications of LT1521CMS8

Regulator TopologyPositive AdjustableVoltage - Output3.8 ~ 20 V
Voltage - Input4.3 ~ 20 VVoltage - Dropout (typical)0.5V @ 300mA
Number Of Regulators1Current - Output300mA
Current - Limit (min)320mAOperating Temperature0°C ~ 125°C
Mounting TypeSurface MountPackage / Case8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
Lead Free Status / RoHS StatusContains lead / RoHS non-compliant  
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LT1521/LT1521-3
LT1521-3.3/LT1521-5
U
U
APPLICATIONS
INFORMATION
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 vary depend-
ing on the conditions. Many battery-powered circuits
incorporate some form of power management. The fol-
lowing information will help optimize battery life. Table 4
summarizes the following information.
The reverse output current will follow the curve in Figure
3 when the input is pulled to ground. This current flows
through the output pin to ground. The state of the shut-
down pin will have no effect on output current when the
input pin is pulled to ground.
In some applications it may be necessary to leave the input
on the LT1521 unconnected when the output is held high.
This can happen when the LT1521 is powered from a
50
T
= 25 C
J
45
V
= 0V
IN
CURRENT FLOWS
40
INTO OUTPUT PIN
V
= V
35
OUT
SENSE
(LT1521-3/LT1521-3.3
30
LT1521-5)
V
= V
(LT1521)
OUT
ADJ
25
LT1521-3.3
20
15
LT1521-3
10
5
0
0
1
2
3
4
5
6
OUTPUT VOLTAGE (V)
Figure 3. Reverse Output Current
12
W
U
rectified AC source. If the AC source is removed, then the
input of the LT1521 is effectively left floating. The reverse
output current also follows the curve in Figure 3 if the input
pin is left open. The state of the shutdown pin will have no
effect on the reverse output current when the input pin is
floating.
When the input of the LT1521 is forced to a voltage below
its nominal output voltage and its output is held high, the
output current will follow the curve shown in Figure 3. This
can happen if the input of the LT1521 is connected to a
discharged (low voltage) battery and the output is held up
by either a backup battery or by second regulator circuit.
When the input pin is forced below the output pin or the
output pin is pulled above the input pin, the input current
will typically drop to less than 2 A (see Figure 4). The state
of the shutdown pin will have no effect on the reverse
output current when the output is pulled above the input.
LT1521
LT1521-5
7
8
9
10
LT1521 • F03
5
V
= 3V (LT1521-3)
OUT
V
= 3.3V (LT1521-3.3)
OUT
V
= 5V (LT1521-5)
4
OUT
LT1521-3.3
3
2
LT1521-3
LT1521-5
1
0
0
1
2
3
4
5
INPUT VOLTAGE (V)
LT1521 • F04
Figure 4. Input Current
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