LT1946A

9

sn1946a 1946afs

Diode Selection

A Schottky diode is recommended for use with the LT1946A.

The Microsemi UPS120 is a very good choice. Where the

input to output voltage differential exceeds 20V, use the

UPS140 (a 40V diode). These diodes are rated to handle an

average forward current of 1A. For applications where the

average forward current of the diode is less than 0.5A, an

ON Semiconductor MBR0520 diode can be used.

Setting Output Voltage

To set the output voltage, select the values of R1 and R2

(see Figure 1) according to the following equation:

RR

V

V

OUT

12

125

1

=









.

–

A good range for R2 is from 5k to 30k.

Layout Hints

The high speed operation of the LT1946A demands careful

attention to board layout. You will not get advertised

performance with careless layouts. Figure 6 shows the

recommended component placement for a boost con-

verter.

1

2

8

7

3

4

6

5

L1

C2

LT1946A

GND

SHUTDOWN

R1

R2

MULTIPLE

VIAs

GROUND PLANE

19949 F04

C1

+

CSS

Figure 6. Recommended Component

Placement for Boost Converter

NOTE: DIRECT HIGH CURRENT PATHS USING WIDE PC TRACES. MINIMIZE TRACE AREA AT

VIAS AT ONE LOCATION ONLY TO AVOID INTRODUCING SWITCHING CURRENTS INTO THE

GROUND PLANE.

FREQUENCY (Hz)

100

50

0

–50

100

10k

100k

1M

1946A FO5a

1k

FREQUENCY (Hz)

0

–100

–200

100

10k

100k

1M

1946A FO5b

1k

–180

58

°

Figure 5. Gain and Phase Plots of Figure 1 Circuit

APPLICATIO S I FOR ATIO