12

LT1676

Figure 4a. Minimum Component Count Application

C1: PANASONIC HFQ

C2: AVX D CASE TPSD107M010R0080

C4, C5: X7R OR COG/NPO

D1: MOTOROLA 100V, 1A, SMD SCHOTTKY

L1: COILCRAFT DO3316P-224

C1

39

µF

63V

1676 F04a

12V TO

48V

+

C2

100

µF

10V

+

D1

MBRS1100

R1

36.5k

1%

5V

0mA to 500mA

R2

12.1k

1%

R3

22k

5%

L1

220

µH

C3

2200pF

X7R

C4

100pF

C5

100pF

R1: 24.3K, R2: 14.7k

L1: 150

µH, DO3316P-154

LT1676

FB

SHDN

SYNC

2

5

4

3

7

8

1

6

GND

1

60

70

80

90

10

100

1000

1676 F04b

50

40

30

20

C1

1676 F05

+

C2

+

D1

R1

R2

R3

L1

C3

R4

210k

1%

R5

6.19k

1%

C4

C5

LT1676

FB

SHDN

SYNC

2

5

4

3

7

8

1

6

GND

Figure 5. User Programmable Undervoltage Lockout

(The 2.5

µA factor is an allowance to minimize error due to

SHDN pin input current.)

Behavior is as follows: Normal operation is observed at the

nominal input voltage of 48V. As the input voltage is

input voltage, typically 18V or so at 25

°C, the voltage on

the SHDN pin will drop to the shutdown threshold, and the

The resistive divider of R4 and R5 will continue to draw

SHDN pin

lockout threshold is relatively accurate includ-

ing temperature effects, the SHDN pin

shutdown thresh-

old is more coarse, and exhibits considerably more

temperature drift. Nevertheless the shutdown threshold

will always be well below the lockout threshold.)