13

LT1308A/LT1308B

1308abfa

so that copper loss is minimized. Acceptable inductance

values range between 2

μH and 20μH, with 4.7μH best for

most applications. Lower value inductors are physically

smaller than higher value inductors for the same current

capability.

Table 1 lists some inductors we have found to perform well

in LT1308A/LT1308B application circuits. This is not an

exclusive list.

Table 1

VENDOR

PART NO.

VALUE

PHONE NO.

Murata

LQH6C4R7

4.7

μH

770-436-1300

Sumida

CDRH734R7

4.7

μH

847-956-0666

Coiltronics

CTX5-1

5

μH

561-241-7876

Coilcraft

LPO2506IB-472

4.7

μH

847-639-6400

Capacitors

Equivalent Series Resistance (ESR) is the main issue

regarding selection of capacitors, especially the output

capacitors.

The output capacitors specified for use with the LT1308A/

LT1308B circuits have low ESR and are specifically

designed for power supply applications. Output voltage

ripple of a boost converter is equal to ESR multiplied by

switch current. The performance of the AVX TPSD227M006

220

μF tantalum can be evaluated by referring to Figure 3.

When the load is 800mA, the peak switch current is

Ripple can be further reduced by paralleling ceramic units.

Table 2 lists some capacitors we have found to perform

well in the LT1308A/LT1308B application circuits. This is

not an exclusive list.

Table 2

VENDOR

SERIES

PART NO.

VALUE

PHONE NO.

AVX

TPS

TPSD227M006

220

μF, 6V 803-448-9411

AVX

TPS

TPSD107M010

100

μF, 10V 803-448-9411

Taiyo Yuden

X5R

LMK432BJ226

22

μF, 10V 408-573-4150

Taiyo Yuden

X5R

TMK432BJ106

10

μF, 25V 408-573-4150

COMPONENT SELECTION

Diodes

We have found ON Semiconductor MBRS130 and Interna-

tional Rectifier 10BQ015 to perform well. For applications

MBRS140 or 10BQ040.

Height limited applications may benefit from the use of the

MBRM120. This component is only 1mm tall and offers

performance similar to the MBRS130.

Inductors

Suitable inductors for use with the LT1308A/LT1308B

must fulfill two requirements. First, the inductor must be

able to handle current of 2A steady-state, as well as

support transient and start-up current over 3A without

inductance decreasing by more than 50% to 60%. Second,

the DCR of the inductor should have low DCR, under 0.05

Ω

Figure 17. Start-Up Waveforms of Figure 16’s Circuit

without Soft-Start Components

Figure 18. Start-Up Waveforms of Figure 16’s Circuit

with Soft-Start Components Added

5V/DIV

50

μs/DIV

1308 F17

1A/DIV

10V/DIV

5ms/DIV

1308 F18

1A/DIV

10V/DIV

12V

5V

12V

5V