1308AI Linear Technology Corporation, 1308AI Datasheet - Page 13

• Manufacturer Part Number: 1308AI
• Description: Lt1308b - Single Cell High Currentmicropower 600khz Boost Dc/dc Converter
• Manufacturer: Linear Technology Corporation

APPLICATIONS
COMPONENT SELECTION
Diodes
We have found ON Semiconductor MBRS130 and Interna-
tional Rectifier 10BQ015 to perform well. For applications
where V
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
5V/DIV
V
V
10V/DIV
10V/DIV
Figure 18. Start-Up Waveforms of Figure 16’s Circuit
with Soft-Start Components Added
Figure 17. Start-Up Waveforms of Figure 16’s Circuit
without Soft-Start Components
OUT
OUT
1A/DIV
1A/DIV
V
V
SHDN
SHDN
12V
12V
I
5V
I
L1
5V
L1
OUT
exceeds 30V, use 40V diodes such as
U
INFORMATION
50μs/DIV
5ms/DIV
U
W
1308 F18
1308 F17
U
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
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
approximately 2A. Output voltage ripple is about 60mV
P
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
, so the ESR of the output capacitor is 60mV/2A or 0.03Ω.
SERIES
TPS
TPS
X5R
X5R
LPO2506IB-472
CDRH734R7
LQH6C4R7
PART NO.
CTX5-1
TPSD227M006
TPSD107M010 100μF, 10V 803-448-9411
LMK432BJ226
TMK432BJ106
PART NO.
LT1308A/LT1308B
VALUE
4.7μH
4.7μH
4.7μH
5μH
220μF, 6V
22μF, 10V
10μF, 25V
VALUE
770-436-1300
847-956-0666
561-241-7876
847-639-6400
803-448-9411
408-573-4150
408-573-4150
PHONE NO.
PHONE NO.
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