LT1308A/LT1308B
U
W U U
APPLICATIONS INFORMATION
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.
12V
VOUT
5V/DIV
5V
IL1
1A/DIV
VSHDN
10V/DIV
Table1listssomeinductorswehavefoundtoperformwell
in LT1308A/LT1308B application circuits. This is not an
exclusive list.
50μs/DIV
1308 F17
Figure 17. Start-Up Waveforms of Figure 16’s Circuit
without Soft-Start Components
Table 1
VENDOR
Murata
PART NO.
LQH6C4R7
CDRH734R7
CTX5-1
VALUE
4.7μH
4.7μH
5μH
PHONE NO.
770-436-1300
847-956-0666
561-241-7876
847-639-6400
12V
Sumida
VOUT
5V
Coiltronics
Coilcraft
LPO2506IB-472
4.7μH
IL1
1A/DIV
VSHDN
10V/DIV
Capacitors
5ms/DIV
1308 F18
Equivalent Series Resistance (ESR) is the main issue
regarding selection of capacitors, especially the output
capacitors.
Figure 18. Start-Up Waveforms of Figure 16’s Circuit
with Soft-Start Components Added
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
switchcurrent.TheperformanceoftheAVXTPSD227M006
220μF tantalum can be evaluated by referring to Figure 3.
When the load is 800mA, the peak switch current is
approximately 2A. Output voltage ripple is about 60mVP-
P,sotheESRoftheoutputcapacitoris60mV/2Aor0.03Ω.
Ripplecanbefurtherreducedbyparallelingceramicunits.
COMPONENT SELECTION
Diodes
WehavefoundONSemiconductorMBRS130andInterna-
tional Rectifier 10BQ015 to perform well. For applications
where VOUT exceeds 30V, use 40V diodes such as
MBRS140 or 10BQ040.
Heightlimitedapplicationsmaybenefitfromtheuseofthe
MBRM120. This component is only 1mm tall and offers
performance similar to the MBRS130.
Table 2 lists some capacitors we have found to perform
well in the LT1308A/LT1308B application circuits. This is
not an exclusive list.
Inductors
Table 2
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
inductancedecreasingbymorethan50%to60%.Second,
theDCRoftheinductorshouldhavelowDCR,under0.05Ω
VENDOR
AVX
SERIES
TPS
PART NO.
VALUE
PHONE NO.
TPSD227M006 220μF, 6V 803-448-9411
TPSD107M010 100μF, 10V 803-448-9411
LMK432BJ226 22μF, 10V 408-573-4150
TMK432BJ106 10μF, 25V 408-573-4150
AVX
TPS
Taiyo Yuden
Taiyo Yuden
X5R
X5R
1308abfa
13
Linear [ Linear ]
