LT1308BCF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1308BCF' PDF : 20 Pages View PDF
LT1308A/LT1308B
APPLICATIONS INFORMATION
12V
VOUT
5V/DIV
5V
IL1
1A/DIV
VSHDN
10V/DIV
50μs/DIV
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Figure 17. Start-Up Waveforms of Figure 16’s Circuit
without Soft-Start Components
12V
VOUT
5V
IL1
1A/DIV
VSHDN
10V/DIV
5ms/DIV
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Figure 18. Start-Up Waveforms of Figure 16’s Circuit
with Soft-Start Components Added
COMPONENT SELECTION
Diodes
We have found ON Semiconductor MBRS130 and Inter-
national Rectifier 10BQ015 to perform well. For applica-
tions where VOUT exceeds 30V, use 40V diodes such as
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 0.05Ω so
that copper loss is minimized. Acceptable inductance
values range between 2μH 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
Murata
Sumida
Coiltronics
Coilcraft
PART NO.
LQH6C4R7
CDRH734R7
CTX5-1
LPO2506IB-472
VALUE
4.7μH
4.7μH
5μH
4.7μH
PHONE NO.
770-436-1300
847-956-0666
561-241-7876
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
220μF tantalum can be evaluated by referring to Figure 3.
When the load is 800mA, the peak switch current is approxi-
mately 2A. Output voltage ripple is about 60mVP-P, so the
ESR of the output capacitor is 60mV/2A or 0.03Ω. 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
AVX
AVX
Taiyo Yuden
Taiyo Yuden
SERIES
TPS
TPS
X5R
X5R
PART NO.
TPSD227M006
TPSD107M010
LMK432BJ226
TMK432BJ106
VALUE
220μF, 6V
100μF, 10V
22μF, 10V
10μF, 25V
PHONE NO.
803-448-9411
803-448-9411
408-573-4150
408-573-4150
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