1.4MHz SOT23 Current-Mode

Step-Up DC-DC Converter

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5

Pin Description

Typical Operating Characteristics (continued)

SHDN

5V/div

OUTPUT

VOLTAGE

5V/div

INDUCTOR

CURRENT

500mA/div

2ms/div

CIRCUIT OF FIGURE 3

STARTUP WAVEFORM

WITH SOFT-START

LX VOLTAGE

5V/div

OUTPUT

VOLTAGE

AC-COUPLED

200mV/div

INDUCTOR

CURRENT

500mA/div

400ns/div

SWITCHING WAVEFORM

600

500

300

400

100

200

0

2.5

4.0

3.0

3.5

4.5

5.0

5.5

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

INPUT VOLTAGE (V)

MAXIMUM OUTPUT

CURRENT DEFINED AT

90% OF NO LOAD

OUTPUT VOLTAGE

PIN

NAME

FUNCTION

1LX

Power Switching Connection. Connect LX to the inductor and output rectifier. Connect components

as close to LX as possible.

2

GND

Ground

3FB

Feedback Input. Connect a resistive voltage-divider from the output to FB to set the output voltage.

See the Setting the Output Voltage section.

4

SHDN

Shutdown Input. Drive SHDN low to turn off the converter. To automatically start the converter,

connect SHDN to IN. Drive SHDN with a slew rate of 0.1V/µs or greater. Do not leave SHDN

unconnected. SHDN draws up to 50µA.

5SS

Soft-Start Input. Connect a soft-start capacitor from SS to GND to soft-start the converter. Leave SS

open to disable the soft-start function. See the Soft-Start section.

6IN

Internal Bias Voltage Input. Connect IN to the input voltage source. Bypass IN to GND with a

1µF or greater capacitor as close to IN as possible.