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

is held high (either by a logic signal or because it is tied

quiescent current through its SW pin. This is fine 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.

Figure 4. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit

LOAD CURRENT (mA)

0

3.0

3.5

4.0

4.5

5.0

5.5

6.0

10

TO START

TO RUN

100

1000

1936 F04a

L = 10μH

LOAD CURRENT (mA)

1

6

7

1936 F04b

5

4

10

100

1000

8

TO START

L = 15μH

TO RUN

RUN

RUN

5V/DIV

500mA/DIV

50μs/DIV

5V/DIV

RUN

5V/DIV

500mA/DIV

5V/DIV

SHDN

GND

1936 F05a

0.5ms/DIV

1936 F05b

RUN

15k

0.22μF

SHDN

GND