10
LT1529
LT1529-3.3/LT1529-5
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micropower device and output transient response will be
a function of output capacitance. See the Transient Re-
sponse curves in the Typical Performance Characteristics.
Larger values of output capacitance will decrease the peak
deviations and provide improved output transient re-
sponse for larger load current deltas. Bypass capacitors,
used to decouple individual components powered by the
LT1529, will increase the effective value of the output
capacitor.
Protection Features
The LT1529 incorporates several protection features which
make it ideal for use in battery-powered circuits. In addi-
tion to the normal protection features associated with
monolithic regulators, such as current limiting and ther-
mal limiting, the device is protected against reverse input
voltages, and reverse voltages from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
15V. Current flow into the device will be limited to less than
1mA (typically less than 100µA) and no negative voltage
will appear at the output. The device will protect both itself
and the load. This provides protection against batteries
that can be plugged in backwards.
For fixed voltage versions of the device, the SENSE pin is
internally clamped to one diode drop below ground. For
the adjustable version of the device, the OUTPUT pin is
internally clamped at one diode drop below ground. If the
OUTPUT pin of an adjustable device, or the SENSE pin of
a fixed voltage device, is pulled below ground, with the
input open or grounded, current must be limited to less
than 5mA.
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
depending on the conditions. Many battery-powered cir-
cuits incorporate some form of power management. The
following information will help optimize battery life. Table
2 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 device to ground. The state of the SHDN pin
will have no effect on output current when the V
IN
pin is
pulled to ground.
Table 2. Fault Conditions
V
IN
PIN SHDN PIN OUTPUT/SENSE PINS
<V
OUT
(Nominal) Open (High) Forced to V
OUT
(Nominal) Reverse Output Current ≈ 15µA (See Figure 3), Input Current ≈ 1µA (See Figure 4)
<V
OUT
(Nominal) Grounded Forced to V
OUT
(Nominal) Reverse Output Current ≈ 15µA (See Figure 3), Input Current ≈ 1µA (See Figure 4)
Open Open (High) > 1V Reverse Output Current ≈ 15µA Peak (See Figure 3)
Open Grounded > 1V Reverse Output Current ≈ 15µA (See Figure 3)
≤0.8V Open (High) ≤0V Output Current = 0
≤0.8V Grounded ≤0V Output Current = 0
>1.5V Open (High) ≤ 0V Output Current = Short-Circuit Current
– 15V < V
IN
< 15V Grounded ≤0V Output Current = 0
OUTPUT VOLTAGE (V)
0
OUTPUT CURRENT (µA)
60
80
100
8
LT1529 • F03
40
20
50
70
90
30
10
0
2
4
6
19
3
5
7
10
LT1529
LT1529-5
LT1529-3.3
T
J
= 25°C, V
IN
= 0V
V
OUT
= V
SENSE
(LT1529-3.3/LT1529-5)
V
OUT
= V
ADJ
(LT1529)
CURRENT FLOWS
INTO DEVICE
Figure 3. Reverse Output Current
