5

LT1507

Inductor Core Loss for 3.3V Output

INDUCTANCE (

µH)

1

0.001

0.1

0.01

1.0

24

6

8

10

LT1507 • TPC17

TYPE 52 POWDERED IRON

Kool M

PERMALLOY

µ = 125

Metglas

®

CORE LOSS IS INDEPENDENT OF LOAD CURRENT

UNTIL LOAD CURRENT FALLS LOW ENOUGH

FOR CIRCUIT TO GO INTO DISCONTINUOUS MODE

Kool M

µ is a registered trademark of Magnetics, Incorporated.

Metglas is a registered trademark of AlliedSignal Incorporated.

BOOST (Pin 1): The BOOST pin is used to provide a drive

voltage, higher than the input voltage, to the internal

bipolar NPN power switch. Without this added voltage the

typical switch voltage loss would be about 1.5V. The

additional boost voltage allows the switch to saturate and

voltage loss approximates that of a 0.3

Ω FET structure,

but with a much smaller die area. Efficiency improves from

70% for conventional bipolar designs to greater than 85%

for these new parts.

with an input voltage between 4.5V and 15V. Under certain

conditions, input voltage may be reduced down to 4V.

Actual minimum operating voltage will always be higher

than the output voltage. It may be limited by switch

OUTPUT VOLTAGE (%)

0

2.5

2.0

1.5

1.0

0.5

0

80

LT1507 • TPC13

20

40

60

100

MOS LOAD

RESISTOR LOAD

CURRENT

SOURCE LOAD

FOLDBACK

CHARACTERISTICS

*POSSIBLE

UNDESIRED

STABLE POINT

FOR CURRENT

SOURCE LOAD

*SEE "MORE THAN JUST VOLTAGE FEEDBACK"

IN APPLICATIONS INFORMATION SECTION

Current Limit Foldback

INPUT VOLTAGE (V)

4

0

0.25

0.50

0.75

1.00

1.25

1.50

6

8

10

12

LT1507 • TPC14

14

L = 10

µH

L = 5

µH

L = 3

µH

L = 2

µH

Maximum Load Current

INPUT VOLTAGE (V)

0

0

0.25

0.50

0.75

1.00

1.25

1.50

369

12

LT1507 • TPC15

15

L = 10

µH

L = 5

µH

L = 20

µH

Maximum Load Current

Boost Pin Current

SWITCH CURRENT (A)

0

12

10

8

6

4

2

0

0.25

0.50

0.75

1.00

LT1507 • TPC16

1.25

Switch Voltage Drop

SWITCH CURRENT (A)

0

0.8

0.6

0.4

0.2

0

0.25

0.50

0.75

1.00

LT1507 • TPC18

1.25

1.50