LT1936 Linear Technology, LT1936 Datasheet - Page 13

• Manufacturer Part Number: LT1936
• Description: 1.4A 500kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

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
6.0
5.5
5.0
4.5
4.0
3.5
3.0
Minimum Input Voltage V
0
V
T
L = 10μH
TO START
TO RUN
A
OUT
= 25°C
Figure 4. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
= 3.3V
LOAD CURRENT (mA)
10
Figure 5. To Soft-Start the LT1936, Add a Resistor and Capacitor to the SHDN Pin.
V
0.22μF
IN
RUN
= 12V, V
15k
RUN
100
OUT
OUT
SHDN
SHDN
= 3.3V, C
GND
GND
= 3.3V
1000
1936 F04a
OUT
= 2 × 22μF , R
500mA/DIV
500mA/DIV
5V/DIV
5V/DIV
5V/DIV
5V/DIV
V
V
RUN
RUN
OUT
OUT
I
I
IN
IN
LOAD
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
is held high (either by a logic signal or because it is tied
to V
quiescent current through its SW pin. This is fi ne if your
system can tolerate a few mA in this state. If you ground
= 3.3Ω
IN
), then the LT1936’s internal circuitry will pull its
0.5ms/DIV
50μs/DIV
8
7
6
5
4
1
Minimum Input Voltage V
V
T
L = 15μH
IN
TO START
A
OUT
TO RUN
= 25°C
pin is allowed to fl oat and the SHDN pin
= 5V
LOAD CURRENT (mA)
10
1936 F05b
1936 F05a
100
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OUT
= 5V
1000
1936 F04b
LT1936
13
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