LT1304CS8 datasheet(7/16 Pages) LINER

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LT1304/LT1304-3.3/LT1304-5

Table 1 lists inductor suppliers along with appropriate part

numbers.

Table 1. Recommended Inductors

VENDOR

SERIES

PHONE NUMBER

Sumida

CD54, CD43

(708) 956-0666

Coiltronics

CTX20-1

(407) 241-7876

Dale

LPT4545

(605) 665-9301

Coilcraft

DO3316, DO1608, DO3308

(708) 639-6400

Capacitor Selection

Low ESR (Equivalent Series Resistance) capacitors should

be used at the output of the LT1304 to minimize output

ripple voltage. High quality input bypassing is also re-

quired. For surface mount applications AVX TPS series

tantalum capacitors are recommended. These have been

specifically designed for switch mode power supplies and

have low ESR along with high surge current ratings. A

100

µF, 10V AVX TPS surface mount capacitor typically

limits output ripple voltage to 70mV when stepping up

from 2V to 5V at a 200mA load. For through hole applica-

tions Sanyo OS-CON capacitors offer extremely low ESR

in a small package size. Again, if peak switch current is

reduced using the ILIM pin, capacitor requirements can be

eased and smaller, higher ESR units can be used. Sug-

gested capacitor sources are listed in Table 2.

Table 2. Recommended Capacitors

VENDOR

SERIES

TYPE

PHONE NUMBER

AVX

TPS

Surface Mount

(803) 448-9411

Sanyo

OS-CON

Through Hole

(619) 661-6835

Sprague

595D

Surface Mount

(603) 225-1961

Diode Selection

Best performance is obtained with a Schottky rectifier

such as the 1N5818. Motorola makes the MBRS130L

Schottky which is slightly better than the 1N5818 and

comes in a surface mount package. For lower switch

currents, the MBR0530 is recommended. It comes in a

very small SOD-123 package. Multiple 1N4148s in parallel

can be used in a pinch, although efficiency will suffer.

OPERATIO

ILIM Function

The LT1304’s current limit (ILIM) pin can be used for soft

start. Upon start-up, the LT1304 will draw maximum

current (about 1A) from the supply to charge the output

capacitor. Figure 3 shows VOUT and VIN waveforms as the

device is turned on. The high current flow can create IR

drops along supply and ground lines or cause the input

supply to drop out momentarily. By adding R1 and C1 as

shown in Figure 4, the switch current is initially limited to

well under 1A as detailed in Figure 5. Current flowing into

C1 from R1 and the ILIM pin will eventually charge C1 and

R1 effectively takes C1 out of the circuit. R1 also provides

a discharge path for C1 when SHUTDOWN is brought low

for turn-off.

VOUT

2V/DIV

IIN

500mA/DIV

VSHDN

10V/DIV

1ms/ DIV

1304 F03

Figure 3. Start-Up Response. Input Current Rises Quickly to

1A. VOUT Reaches 5V in Approximately 1ms. Output Drives

20mA Load

Figure 4. 2-Cell to 5V/200mA Boost Converter Takes Four

External Parts. Components with Dashed Lines Are for

Soft Start (Optional)

VIN

GND

ILIM

SENSE

LBI

SHDN

LB0

LT1304-5

100

µF

100

µF

2 CELLS

µH*

MBRS130L

200mA

*SUMIDA CD54-220

1304 F04

SHUTDOWN

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