LT1129/LT1129-3.3/LT1129-5
U U
U
W
APPLICATIO S I FOR ATIO
Insomeapplicationsitmaybenecessarytoleavetheinput
to the LT1129 unconnected when the output is held high.
This can happen when the LT1129 is powered from a
rectified AC source. If the AC source is removed, then the
input of the LT1129 is effectively left floating. The reverse
outputcurrentalsofollowsthecurveinFigure3iftheinput
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 LT1129 is forced to a voltage below
its nominal output voltage and its output is held high, the
reverse output current will still follow the curve shown in
Figure 3. This can happen if the input of the LT1129 is
connected to a discharged (low voltage) battery and the
output is held up by either a backup battery or by a 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 2µA (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.
100
5
T
= 25°C
J
V
V
= 3.3V (LT1129-3.3)
= 5V (LT1129-5)
OUT
OUT
90
80
V
= 0V
IN
SENSE
V
= V
OUT
4
3
2
1
0
CURRENT FLOWS
70 INTO DEVICE
60
50
40
30
20
10
0
LT1129
LT1129-3.3
LT1129-5
0
2
4
6
8
10
1
3
1
3
5
7
9
0
2
4
5
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1129 F03
1129 F04
Figure 3. Reverse Output Current
Figure 4. Input Current
Table 4. Fault Conditions
INPUT PIN
SHDN PIN
OUTPUT PIN
< V
(Nominal)
Open (Hi)
Forced to V
(Nominal)
Reverse Output Current ≈ 15µA (See Figure 3)
Input Current ≈ 1µA (See Figure 4)
OUT
OUT
< V
(Nominal)
Grounded
Forced to V
(Nominal)
Reverse Output Current ≈ 15µA (See Figure 3)
Input Current ≈ 1µA (See Figure 4)
OUT
OUT
Open
Open
Open (Hi)
Grounded
Forced to V
Forced to V
(Nominal)
(Nominal)
Reverse Output Current ≈ 15µA (See Figure 3)
Reverse Output Current ≈ 15µA (See Figure 3)
OUT
OUT
112935fc
12
Linear Systems [ Linear Systems ]
