LT1946

8

sn1946 1946fs

APPLICATIO S I FOR ATIO

Diode Selection

A Schottky diode is recommended for use with the LT1946.

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 LT1946 demands careful

attention to board layout. You will not get advertised

performance with careless layout. Figure 6 shows the

recommended component placement for a boost

converter.

FREQUENCY (Hz)

0

50

100

100

10k 25k

100k

1M

1946 F05a

–50

1k

FREQUENCY (Hz)

–100

0

100

10k 25k

100k

1M

1946 F05b

–200

–180

1k

60

°

Figure 5. Bode Plot of Figure 1’s Circuit

Figure 6. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize

Introducing Switching Currents Into the Ground Plane

1

2

8

7

3

4

6

5

L1

C2

LT1946

GND

SHUTDOWN

R1

R2

MULTIPLE

VIAs

GROUND PLANE

1946 F06

C1

+