3A, 2MHz Step-Down Regulator

with Integrated Switches

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7

Pin Description

PIN

NAME

FUNCTION

1

PREBIAS

Leave pin unconnected to prevent discharging of output capacitor during soft-start. Connect to GND

otherwise. (See the Soft-Starting into a Prebiased Output section.)

Ω resistor. Connect a 1µF ceramic

3, 4

CTL1,

CTL2

Preset Output Voltage Selection Input. CTL1 and CTL2 set the output voltage to one of nine preset

voltages. See Table 1 for preset voltages.

5

REFIN

External Reference Input. Connect REFIN to SS to use the internal 0.6V reference. Connecting REFIN to an

external reference voltage forces FB to regulate the voltage applied to REFIN. REFIN is internally pulled to

GND when the IC is in shutdown mode.

6SS

Soft-Start Input. Connect a capacitor from SS to GND to set the startup time. See the Soft-Start and REFIN

section for details on setting the soft-start time.

7

GND

Analog Circuit Ground

8

COMP

Output of the Voltage-Error Amplifier. Connect the necessary compensation network from COMP to FB.

COMP is internally pulled to GND when the IC is in shutdown mode.

9FB

Feedback Input. Connect FB to the center tap of an external resistor-divider from the output to GND to set

CTL1 and CTL2 to select any of nine preset voltages.

10

OUT

Output Voltage Sense. Connect to the output. Leave OUT unconnected when an external resistor-divider

is used.

11

FREQ

Oscillator Frequency Selection. Connect a resistor from FREQ to GND to select the switching frequency.

12

PWRGD

13

BST

High-Side MOSFET Driver Supply. Bypass BST to LX with a 0.1µF capacitor.

14, 15, 16

LX

Inductor Connection. All LX pins are internally connected together. Connect all LX pins to the output

inductor. LX is high impedance when the IC is in shutdown mode.

17–20

PGND

Power Ground. Connect all PGND pins externally to the power ground plane.

21, 22, 23

IN

Power-Supply Input. Input supply range is from 2.35V to 3.6V. Bypass with 22µF ceramic capacitance to

PGND externally. See the Typical Application Circuit.

24

EN

Enable Input. Logic input to enable/disable the MAX8643A.

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EP

Exposed Paddle. Connect to a large ground plane to optimize thermal performance.