LT1308BCS8#PBF Linear Technology, LT1308BCS8#PBF Datasheet - Page 12

• Manufacturer Part Number: LT1308BCS8#PBF
• Description: IC DC/DC CONV SINGLE CELL 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LT1308BCS8#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 1A
• Frequency - Switching: 600kHz
• Voltage - Input: 1 ~ 10 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Primary Input Voltage: 6V
• No. Of Outputs: 1
• Output Voltage: 34V
• Output Current: 1A
• No. Of Pins: 8
• Operating Temperature Range: 0°C To +70°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Range: 1V To 10V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LT1308A/LT1308B
Soft-Start
In some cases it may be undesirable for the LT1308A/
LT1308B to operate at current limit during start-up, e.g.,
12
Figure 15. 5V SEPIC Start-Up from 9V Input into 10Ω Load
1V/DIV
2A/DIV
5V/DIV
2V/DIV
2A/DIV
5V/DIV
V
V
V
SHDN
SHDN
V
OUT
OUT
I
I
SW
L1
Figure 14. 5V Boost Converter of Figure 1.
Start-Up from 3V Input into 5Ω Load
Figure 16. 5V to 12V Boost Converter with Soft-Start Components Q1, C4, R3 and R4
V
500μs/DIV
500μs/DIV
5V
IN
+
C1: AVX TAJ476M010
C2: TAIYO YUDEN TMK432BJ106MM
D1: IR 10BQ015
L1: MURATA LQH6C4R7
Q1: 2N3904
C1
47μF
R3
33k
C4
33nF
SHUTDOWN
1308 F14
1308 F15
Q1
33k
R4
SHDN
V
V
IN
C
SOFT-START
COMPONENTS
R
47k
LT1308B
C
C
100pF
4.7μH
C
L1
when operating from a battery composed of alkaline cells.
The inrush current may cause suffi ciency internal voltage
drop to trigger a low-battery indicator. A programmable
soft-start can be implemented with 4 discrete compo-
nents. A 5V to 12V boost converter using the LT1308B
is detailed in Figure 16. C4 differentiates V
a current to fl ow into R3 as V
current exceeds 0.7V/33k, or 21μA, current fl ows into
the base of Q1. Q1’s collector then pulls current out the
V
is limited as follows:
With C4 = 33nF , V
waveforms for Figure 16’s circuit are pictured in Figure 17.
Without the soft-start circuit implemented, the inrush cur-
rent reaches 3A. The circuit reaches fi nal output voltage in
approximately 250μs. Adding the soft-start components
reduces inductor current to less than 1A, as detailed in
Figure 18, while the time required to reach fi nal output
voltage increases to about 15ms. C4 can be adjusted to
achieve any output slew rate desired.
GND
SW
C
pin, creating a feedback loop where the slope of V
ΔV
FB
Δt
OUT
D1
10k
=
33k • C4
0.7V
100k
OUT
/t is limited to 640mV/ms. Start-up
11.3k
330pF
1308 F16
C2
10μF
OUT
V
12V
500mA
OUT
increases. When this
OUT
, causing
1308abfb
OUT