LT1300CS8 Linear Technology, LT1300CS8 Datasheet - Page 6

• Manufacturer Part Number: LT1300CS8
• Description: IC DC/DC CONV STP-UP HI-EFF8SOIC
• Manufacturer: Linear Technology
• Type: Step-Up (Boost)r

Specifications of LT1300CS8

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 5V
• Current - Output: 220mA
• Frequency - Switching: 155kHz
• Voltage - Input: 1.8 ~ 10 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Power - Output: 500mW
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
LT1300
Output Voltage Selection
The LT1300 can be selected to 3.3V or 5V under logic
control or fixed at either by tying SELECT to ground or V
respectively. It is permissible to tie SELECT to a voltage
higher than V
Efficiency in 3.3V mode will be slightly less that in 5V mode
due to the fact that the diode drop is a greater percentage
of 3.3V than 5V. Since the bipolar switch in the LT1300
gets its base drive from V
efficiency occurs when in 3.3V mode. When V
the programmed output voltage the output will follow the
input. This is characteristic of the simple step-up or
“boost” converter topology. A circuit example that pro-
vides a regulated output with an input voltage above or
below the output (called a buck-boost or SEPIC) is shown
in the Typical Applications section.
Shutdown
The converter can be turned off by pulling SHDN (pin 3)
high. Quiescent current drops to 10 A in this condition.
Bias current of 3 A to 5 A flows into the pin (at 2.5V input).
It is recommended that SHDN not be left floating. Tie the
pin to ground if the feature is not used.
I
The LT1300’s current limit (I
start. Upon start-up, switching regulators require maxi-
mum current from the supply. The high currents flowing
can create IR drops along supply and ground lines and
are especially demanding on alkaline batteries. By in-
stalling an R1 and C3 as shown in Figure 4, the switch
current in the LT1300 is limited to 400mA until the 15 A
flowing out of the I
tor. Input current is held to under 500mA while the
output voltage ramps up to 5V as shown in Figure 5. The
1Meg resistor provides a discharge path for the capacitor
without appreciably decreasing peak switch current. When
the full capability of the LT1300 is not required, peak
current can be reduced by changing the value of R3 as
shown in Figure 6. With R3 = 0, switch current is limited
to approximately 400mA.
6
LIM
Function
IN
as long as it does not exceed 10V.
U
LIM
pin charges up the 0.1 F capaci-
INFORMATION
U
LIM
IN
, no reduction in switch
) pin can be used for soft
W
IN
U
exceeds
IN
Figure 4. Addition of R1 and C3 Limit Input Current at Startup
500mA/DIV
I
10V/DIV
BATTERY
2VDIV
V
Figure 5. Startup Waveforms using Soft-Start Circuitry
+
V
SHDN
OUT
C1
100µF
Figure 6. Peak Switch Current vs. R
1100
1000
900
800
700
600
500
400
300
I
LOAD
100
SELECT
PGND
SHDN
V
1.6V V IN 5V
IN
= 100mA, V
LT1300
10µH
L1
1k
REP RATE = 1Hz
SENSE
500 s/DIV
GND
SW
I
LIM
R
LIM
OUT
10k
( )
= 5V
R1
1M
100k
D1
LT1300 F1B
C3
0.1µF
LIM
1M
+
LT1300 F5
C2
100µF
5V/3.3V
OUTPUT