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ManualsBrandsLINEAR TECHNOLOGY ManualsVoltage RegulatorsLT1936EMS8E#PBF
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LT1936
13
1936fd
APPLICATIONS INFORMATION
RC time constant, the peak start-up current can be reduced
to the current that is required to regulate the output, with
no overshoot. Choose the value of the resistor so that it
can supply 60μA when the SHDN pin reaches 2.3V.
Shorted and Reversed Input Protection
If the inductor is chosen so that it won’t saturate exces-
sively, an LT1936 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT1936 is absent. This may occur in battery charging ap-
plications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT1936’s
output. If the V
IN
pin is allowed to fl oat and the SHDN pin
is held high (either by a logic signal or because it is tied
to V
IN
), then the LT1936’s internal circuitry will pull its
quiescent current through its SW pin. This is fi ne if your
system can tolerate a few mA in this state. If you ground
Figure 5. To Soft-Start the LT1936, Add a Resistor and Capacitor to the SHDN Pin.
V
IN
= 12V, V
OUT
= 3.3V, C
OUT
= 2 × 22μF, R
LOAD
= 3.3Ω
Figure 4. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
Minimum Input Voltage V
OUT
= 3.3V
Minimum Input Voltage V
OUT
= 5V
LOAD CURRENT (mA)
0
3.0
INPUT VOLTAGE (V)
3.5
4.0
4.5
5.0
5.5
6.0
10
TO START
TO RUN
100 1000
1936 F04a
V
OUT
= 3.3V
T
A
= 25°C
L = 10μH
LOAD CURRENT (mA)
1
INPUT VOLTAGE (V)
6
7
1936 F04b
5
4
10 100 1000
8
TO START
V
OUT
= 5V
T
A
= 25°C
L = 15μH
TO RUN
RUN
RUN
5V/DIV
I
IN
500mA/DIV
50μs/DIV
V
OUT
5V/DIV
RUN
5V/DIV
I
IN
500mA/DIV
V
OUT
5V/DIV
SHDN
GND
1936 F05a
0.5ms/DIV
1936 F05b
RUN
15k
0.22μF
SHDN
GND
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