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LT1777

TYPICAL APPLICATIONS

Basic 3.3V Output Application

Figure 10 shows a circuit similar to the previous example,

but modified for a 3.3V output. Once again, Efficiency and

Internal Power Dissipation graphs are shown in Figure 11

for input voltages of 12V, 24V and 36V, and for sense

inductor values of 0

µH, 1µH and 2.2µH. It is interesting to

note that internal LT1777 dissipation is very close to the

5V example. This confirms the fact that internal LT1777

dissipation is largely determined by input voltage, load

current and sense inductor, and is only a weak function of

output voltage.

The data as shown were performed using an off-the-shelf

Coilcraft DO3316-154 as the main inductor. This is a cost-

effective inductor using an open style of construction. For

a toroidal style inductor, the Coiltronics CTX150-4 or

similar may be substituted.

VIN

VCC

VSW

LT1777

SHDN

SYNC

µH TO 2.2µH

(SEE BELOW)

150

µH

100

µF

10V

20k

1777 F10

VOUT

3.3V

12.1k

VIN

10V TO 40V

SGND

µF

63V

12k

2200pF

100pF

C1: PANASONIC HFQ ELECTROLYTIC

C2: AVX D CASE TPSD107M010R0080

C3, C4, C5: NPO OR X7R

C6, C7: Z5U

D1: MOTOROLA 100V, 1A SMD SCHOTTKY

MBRS1100

L1: SENSE INDUCTOR CAN VARY FROM 0

µH TO 2.2µH

AS PER APPLICATION. GRAPHICAL DATA TAKEN WITH:

µH = D01608C-102, COILCRAFT OR SIMILAR

2.2

µH = D01608C-222, COILCRAFT OR SIMILAR (SEE TEXT)

L2: COILCRAFT D03316-154 OR SIMILAR (SEE TEXT)

100pF

0.1

µF

0.1

µF

Figure 10. Basic 3.3V Output Application

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