LT3506 datasheet(13/24 Pages) LINER

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LT3506/LT3506A

3506afb

ILOAD (A)

0.001

4.0

4.5

3506 G14

3.5

3.0

0.01

0.1

5.5

5.0

VIN TO START

BOOST DIODE

TIED TO OUTPUT

BOOST DIODE

TIED TO INPUT

VIN TO RUN

TA = 25°C

DBOOST = 1N5817

ILOAD (A)

0.001

5.5

6.0

3506 G15

5.0

4.5

0.01

0.1

7.0

6.5

VIN TO START

BOOST DIODE

TIED TO OUTPUT

BOOST DIODE

TIED TO INPUT

VIN TO RUN

TA = 25°C

DBOOST = 1N5817

The minimum input voltage of an LT3506 application is

limited by the minimum operating voltage (<3.6V) and by

the maximum duty cycle as outlined above. For proper

start-up, the minimum input voltage is also limited by

the boost circuit. If the input voltage is ramped slowly,

or the LT3506 is turned on with its RUN/SS pin when the

output is already in regulation, then the boost capacitor

may not be fully charged. Because the boost capacitor is

charged with the energy stored in the inductor, the circuit

will rely on some minimum load current to get the boost

circuit running properly. This minimum load will depend

on input and output voltages, and on the arrangement of

the boost circuit. The minimum load generally goes to

zero once the circuit has started. The plots below show

the minimum load current to start and to run as a function

of input voltage for 3.3V and 5V outputs. In many cases

the discharged output capacitor will present a load to the

switcher which will allow it to start. The plots show the

worst-case situation where VIN is ramping very slowly.

Use a Schottky diode (such as the BAT-54) for the lowest

start-up voltage.

Minimum Input Voltage,

VOUT = 3.3V (LT3506A)

Minimum Input Voltage,

VOUT = 5V (LT3506A)

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