4

LT1108

CC

HARA TERISTICS

A

TYPICALPERFOR

CE

GND (Pin 5): Ground.

AO (Pin 6): Auxiliary gain block (GB) output. Open collector,

can sink 100

µA.

SET (Pin 7): GB input. GB is an op amp with positive input

connected to SET pin and negative input connected to

1.245V reference.

FB/SENSE (Pin 8): On the LT1108 (adjustable) this pin

goes to the comparator input. On the LT1108-5 and

LT1108-12, this pin goes to the internal application resistor

that sets output voltage.

Oscillator Frequency

Duty Cycle

Switch-ON Time

TEMPERATURE (°C)

13

14

16

17

18

22

LT1108 • TPC07

15

19

20

21

–50

25

75

–25

0

50

100

TEMPERATURE (°C)

50

55

60

65

70

80

LT1108 • TPC08

75

–50

25

75

–25

0

50

100

Minimum/Maximum Frequency

Switch Saturation Voltage

Switch Saturation Voltage

vs ON-Time

Step-Up Mode

Step-Down Mode

PI

FU C

S

TI

lower current limit is desired, connect a resistor between

to approximately 400mA.

SW1 (Pin 3): Collector of power transistor. For step-up

mode connect to inductor/diode. For step-down mode

SW2 (Pin 4): Emitter of power transistor. For step-up

mode connect to ground. For step-down mode connect to

inductor/diode. This pin must never be allowed to go more

than a Schottky diode drop below ground.

TEMPERATURE (˚C)

–50

38

40

42

25

75

LT1108 • TPC09

36

34

–25

0

50

100

32

30

44

TEMPERATURE (°C)

–50

0.3

0.4

0.5

25

75

LT1108 • TPC11

0.2

0.1

0

–25

0

50

0.6

0.7

0.8

100

TEMPERATURE (°C)

–50

0.8

1.0

1.1

1.2

1.3

1.4

1.5

–25

0

25

50

LT1108 • TPC12

75

1.6

1.7

1.8

0.9

100

ON-TIME (

µs)

25

20

24

28

45

LT1108 • TPC10

16

12

0

30

35

40

50

18

22

26

14

10