8

LT1931/LT1931A

1931fa

increased to 68nF, resulting in a lower peak input current

be increased further for an even slower ramp, if desired.

driven low to shut down the device. D2 can be omitted,

resulting in a “soft-stop” slow discharge of the output

capacitor.

1

2

3

5

4

C2

D1

R2

R1

L1B

C1

L1A

+

SHUTDOWN

1931 F10

GND

C3

2V/DIV

0.5A/DIV

AC COUPLED

5V

0V

200

µs/DIV

1931 F08

Input Current Peaks at 500mA

2V/DIV

0.5A/DIV

AC COUPLED

5V

0V

500

µs/DIV

1931 F09

Input Current Peaks at 350mA

Figure 10. Suggested Component Placement.

Note Cut in Ground Copper at D1’s Cathode

APPLICATIO S I FOR ATIO

DIODE SELECTION

A Schottky diode is recommended for use with the LT1931/

LT1931A. The Motorola MBR0520 is a very good choice.

Where the input to output voltage differential exceeds 20V,

use the MBR0530 (a 30V diode). These diodes are rated to

handle an average forward current of 0.5 A. In applications

where the average forward current of the diode exceeds

0.5A, a Microsemi UPS5817 rated at 1A is recommended.

LAYOUT HINTS

The high-speed operation of the LT1931/LT1931A de-

mands careful attention to board layout. You will not get

advertised performance with careless layout. Figure 10

shows the recommended component placement. The

ground cut at the cathode of D1 is essential for low noise

operation.