High-Frequency, High-Power, Low-Noise,

Step-Up DC-DC Converter

8

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Pin Description

PIN

NAME

FUNCTION

1

ONB

Shutdown Input. When

ONB = high and ONA = low, the device turns off (Table 1).

2

ONA

On-Control Input. When ONA = high or

ONB = low, the device turns on (Table 1).

3, 4, 5

LX

Drain of N-Channel Power Switch. Connect pins 3, 4, and 5 together with wide traces. Connect

6, 9

GND

Ground

7

SS/LIM

Soft-Start and/or Current-Limit Input. Connect a capacitor from SS/LIM to GND to control the

rate at which the device reaches current limit (soft-start). To reduce the current limit from the

preset values, connect a resistor from SS/LIM to GND (see Design Procedure). During

shutdown, SS/LIM is internally pulled to GND to discharge the soft-start capacitor.

8

REF

Voltage Reference Output. Bypass with a 0.22µF capacitor to GND. Maximum REF load is

50µA.

10

OUT

Output Voltage Sense Input. The device is powered from OUT. Bypass with a 0.1µF capacitor

to PGND with less than 5mm trace length. Connect a 2

Ω series resistor from the output filter

capacitor (0.1µF) to OUT (Figure 1).

11

FB

DC-DC Converter Feedback Input. Connect FB to GND for internally set output voltage (see

3.3/5 pin description). Connect a resistor-divider from the output to set the output voltage in the

+2.5V to +5.5V range. FB regulates to +1.24V (Figure 4).

12, 13, 14

PGND

Power Ground, Source of N-Channel Power MOSFET Switch. Connect pins 12, 13, and 14

together with wide traces.

15

3.3/5

Output Voltage Selection Input. When FB is connected to GND, the regulator uses internal

feedback to set the output voltage.

3.3/5 = low sets output to 3.3V; 3.3/5 = high sets output to

5V. If an external divider is used at FB, connect

3.3/5 to ground.

16

CLK

Clock Input for the DC-DC Converter. Connect to OUT for internal oscillator. Drive CLK with

an external clock for external synchronization.