LT1936
APPLICATIO S I FOR ATIO
Minimum Input Voltage V
OUT
= 3.3V
6.0
5.5
INPUT VOLTAGE (V)
5.0
4.5
4.0
3.5
3.0
0
10
100
LOAD CURRENT (mA)
1000
1936 G14
V
OUT
= 3.3V
T
A
= 25°C
L = 10µH
INPUT VOLTAGE (V)
TO START
TO RUN
Figure 4. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
RUN
SHDN
GND
RUN
15k
SHDN
0.22µF
GND
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
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
U
Minimum Input Voltage V
OUT
= 5V
8
V
OUT
= 5V
T
A
= 25°C
L = 15µH
TO START
7
6
TO RUN
5
4
1
100
10
LOAD CURRENT (mA)
1000
1936 G13
W
U
U
RUN
5V/DIV
I
IN
500mA/DIV
V
OUT
5V/DIV
50µs/DIV
1936 F05a
RUN
5V/DIV
I
IN
500mA/DIV
V
OUT
5V/DIV
0.5ms/DIV
1936 F05b
where the output will be held high when the input to the
LT1936 is absent. This may occur in battery charging
applications 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 float 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 fine if your
system can tolerate a few mA in this state. If you ground
1936fa
13
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