3

LT1931/LT1931A

1931fa

TYPICAL PERFOR A CE CHARACTERISTICS

Quiescent Current

TEMPERATURE (

°C)

–50

4.5

5.0

5.5

25

75

1931 G01

4.0

3.5

3.0

–25

0

50

6.0

6.5

7.0

100

NOT SWITCHING

LT1931A

LT1931

TEMPERATURE (

°C)

–50

–1.28

–1.27

–1.26

–1.25

–1.24

–1.22

–25

025

50

1931 G02

75

100

–1.23

SHDN PIN VOLTAGE (V)

0

–10

10

30

50

1

2

34

1931 G03

5

70

90

0

20

40

60

80

6

LT1931A

LT1931

Feedback Pin Voltage

Shutdown Pin Current

Current Limit

Switch Saturation Voltage

Oscillator Frequency

DUTY CYCLE (%)

10

0.8

1.2

90

1931 G04

0.4

0

30

50

70

20

40

60

80

1.6

0.6

1.0

0.2

1.4

SWITCH CURRENT (A)

0

0

0.05

0.15

0.20

0.25

0.8

0.45

1931 G05

0.10

0.4

0.2

1.0

0.6

1.2

0.30

0.35

0.40

TEMPERATURE (

°C)

–50

0.5

0.9

1.3

1.7

–25

0

25

50

1931 G06

75

2.1

2.5

0.7

1.1

1.5

1.9

2.3

100

LT1931A

LT1931

PI FU CTIO S

SW (Pin 1): Switch Pin. Connect inductor/diode here.

Minimize trace area at this pin to keep EMI down.

GND (Pin 2): Ground. Tie directly to local ground plane.

NFB (Pin 3): Feedback Pin. Reference voltage is –1.255V.

Connect resistive divider tap here. Minimize trace area.

The NFB bias current flows out of the pin. Set R1 and R2

according to:

For LT

R

V

R

OUT

1931 1

1 255

1 255

2

:

|| – .

.

•

–

=

+

()

For LT

A R

V

R

OUT

1931

1

1 255

1 255

2

:

|| – .

.

•

–

=

+

()

SHDN (Pin 4): Shutdown Pin. Tie to 2.4V or more to enable

device. Ground to shut down.