8

LT1303/LT1303-5

LT1303 F08

PHONE

VENDOR

SERIES

TYPE

NUMBERS

AVX

TPS

Surface Mount

(803) 448-9411

Sanyo

OS-CON

Through-Hole

(619) 661-6835

Panasonic

HFQ

Through-Hole

(201) 348-5200

Sprague

595D

Surface Mount

(603) 224-1961

Table 2. Recommended Capacitors

Capacitor Selection

Input and output capacitors should have low ESR for best

efficiency. Recommended capacitors include AVX TPS

series, Sprague 595D series, and Sanyo OS-CON. The

output capacitor’s ESR determines the high frequency

ripple amplitude. A 100

µF capacitor is the minimum rec-

ommended for a 5V output. Higher output voltages can use

lower capacitance values. For example, a 12V output can

use a 33

should be decoupled with a 47

µF or 100µF capacitor at the

pin. When driving a transformer, an additional decoupling

network of 10

Ω and 0.1µF ceramic is recommended as

shown in Figure 10.

Diode Selection

The LT1303’s high switching speed demands a high speed

rectifier. Schottky diodes are preferred for their low for-

ward drop and fast recovery. Suitable choices include the

1N5817, MBRS120LT3, and MBR0520LT1. Do not use

signal diodes such as 1N4148. They cannot carry 1A

current. Also avoid “general-purpose” diodes such as

1N4001. These are far too slow and are unsuitable for any

switching regulator application. For high temperature

applications a silicon diode such as the MUR105 will have

less leakage.

LT1303 F09

Figure 9. Slight Exponential Shape to Inductor Current

Waveform Indicates Excessive DC Resistance

+

47

µF

0.1

µF

CERAMIC

10

Ω

• • •

LT1303 F10

SW

GND

PGND

LT1303

Figure 10. 10

Additional Decoupling. Recommended When Driving

Transformers.