7

LT1930/LT1930A

Figure 5. Transient Response of Step-Up Converter with 33

µF

Tantalum Output Capacitor and No Phase Lead Capacitor

0.2V/DIV

AC COUPLED

0.5A/DIV

AC COUPLED

250mA

150mA

LOAD

CURRENT

200

µs/DIV

1930 F04

DIODE SELECTION

A Schottky diode is recommended for use with the LT1930/

LT1930A. The Motorola MBR0520 is a very good choice.

Where the switch voltage exceeds 20V, use the MBR0530

(a 30V diode). Where the switch voltage exceeds 30V, use

the MBR0540 (a 40V diode). These diodes are rated to

handle an average forward current of 0.5A. In applications

where the average forward current of the diode exceeds

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

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

1 255

1

=









.

–

A good value for R2 is 13.3k which sets the current in the

resistor divider chain to 1.255V/13.3k = 94.7

µA.

Figure 6. Suggested Layout

R1

R2

GND

C3

C2

L1

D1

C1

SHUTDOWN

1930 F06

+

GND

SW

SHDN

FB

16V

4

51

3

D1

L1

2

R1

LT1930

1930 F07

C2

C1

121k

R2

Figure 7. Keeping SHDN Below 10V

LAYOUT HINTS

The high speed operation of the LT1930/LT1930A

demands careful attention to board layout. You will not get

advertised performance with careless layout. Figure 6

shows the recommended component placement.

Driving SHDN Above 10V

The maximum voltage allowed on the SHDN pin is 10V. If

you wish to use a higher voltage, you must place a resistor

in series with SHDN. A good value is 121k. Figure 7 shows

The voltage on the SHDN pin is kept below 10V.