lt1129cst-5-pbf Linear Technology Corporation, lt1129cst-5-pbf Datasheet - Page 12

• Manufacturer Part Number: lt1129cst-5-pbf
• Description: 700ma Micropower Low Dropout Regulator With Shutdown
• Manufacturer: Linear Technology Corporation

LT1129/LT1129-3.3/LT1129-5
APPLICATIO S I FOR ATIO
In some applications it may be necessary to leave the input
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
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.
12
Table 4. Fault Conditions
< V
< V
INPUT PIN
OUT
OUT
Open
Open
(Nominal)
(Nominal)
100
90
80
70
60
50
40
30
20
10
0
0
T
V
V
CURRENT FLOWS
INTO DEVICE
Figure 3. Reverse Output Current
J
IN
SENSE
= 25°C
1
= 0V
2
= V
U
OUT
OUTPUT VOLTAGE (V)
3
SHDN PIN
Grounded
Grounded
Open (Hi)
Open (Hi)
LT1129-3.3
4
U
LT1129
5
LT1129-5
6
7
Forced to V
Forced to V
Forced to V
Forced to V
W
8
OUTPUT PIN
9
1129 F03
10
OUT
OUT
OUT
OUT
(Nominal)
(Nominal)
(Nominal)
(Nominal)
U
Reverse Output Current ≈ 15μA (See Figure 3)
Input Current ≈ 1μA (See Figure 4)
Reverse Output Current ≈ 15μA (See Figure 3)
Input Current ≈ 1μA (See Figure 4)
Reverse Output Current ≈ 15μA (See Figure 3)
Reverse Output Current ≈ 15μA (See Figure 3)
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.
5
4
3
2
1
0
0
V
V
OUT
OUT
= 3.3V (LT1129-3.3)
= 5V (LT1129-5)
1
Figure 4. Input Current
INPUT VOLTAGE (V)
2
3
4
1129 F04
5
112935fd