14

LT1676

Minimum Size Inductor Application

Figure 4a employs power path parts that are capable of

delivering the full rated output capability of the LT1676.

Potential users with low output current requirements may

be interested in substituting a physically smaller and less

costly power inductor. The circuit shown on the last page

of this data sheet is topologically identical to the basic

application, but specifies a much smaller inductor, and, a

somewhat smaller input electrolytic capacitor. This circuit

is capable of delivering up to 150mA at 5V, or, up to 200mA

at 3.3V. The only disadvantage is that due to the increased

resistance in the inductor, the circuit is no longer capable

of withstanding indefinite short circuits to ground. The

this will overheat the inductor. Momentary short circuits

of a few seconds or less can still be tolerated.

(a)

(b)

1

60

70

80

90

10

100

1000

1676 F07b

50

40

30

20

C1

NC

Q1

PN2484

Q2

2N2369

1676 F07a

U2

LTC1440

REF

HYST

OUT

3

7

1

2

4

6

5

8

GND

+

C2

+

D1

R1

39k

5%

5V

R2

10k

5%

R5

22k

R6

2.4M

L1

R3

323k

1%

R4

100k

1%

C3

100pF

R7

10M

C1: PANASONIC HFQ 39

µF AT 63V

C2: AVX D CASE 100

µF 10V

TPSD107M010R0080

D1: MOTOROLA 100V, 1A,

SMD SCHOTTKY

MBRS1100 (T3)

L1: COILCRAFT DO3316-224

U1

LT1676

FB

SHDN

SYNC

2

5

4

3

7

8

6

1

GND

Figure 7. Burst Mode Operation Configuration for High Efficiency at Light Load

to maintain proper short-circuit protection. Transistors

current voltage regulator to power U2.

Burst Mode Operation Configuration with UVLO

Figure 7a uses an external comparator to control the

LT1676 via its SHDN pin. As such, the user’s ability to set

an undervoltage lockout (UVLO) threshold with a resistor

is regained in the slightly more complicated circuit shown

in Figure 8.

A dual comparator, the LTC1442, replaces the previous

single comparator. The second comparator monitors a

(user-adjustable) UVLO function. The two comparator

outputs are logically combined in a CMOS NOR gate (U3)

to drive the LT1676 SHDN pin.