LT1129IS8 Просмотр технического описания (PDF) - Linear Integrated System
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LT1129IS8 Datasheet PDF : 16 Pages
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LT 1129/LT 1129-3.3/LT 1129-5
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.
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
TJ = 25°C
90 VIN = 0V
80 VSENSE = VOUT
CURRENT FLOWS
70 INTO DEVICE
60
LT1129
50
40
LT1129-3.3
30
20
LT1129-5
10
0
012345 678
OUTPUT VOLTAGE (V)
9 10
1129 F03
Figure 3. Reverse Output Current
5
VOUT = 3.3V (LT1129-3.3)
VOUT = 5V (LT1129-5)
4
3
2
1
0
0
1
2
3
4
5
INPUT VOLTAGE (V)
1129 F04
Figure 4. Input Current
Table 4. Fault Conditions
INPUT PIN
SHDN PIN
< VOUT (Nominal)
Open (Hi)
< VOUT (Nominal)
Grounded
Open
Open (Hi)
Open
Grounded
OUTPUT PIN
Forced to VOUT (Nominal)
Forced to VOUT (Nominal)
Forced to VOUT (Nominal)
Forced to VOUT (Nominal)
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)
12
112935fc
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