Constant On-Time Buck Converter

With Integrated Linear Regulator

A4402

3

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Functional Block Diagram

ENB

VO2

NPOR

Internal

Regulator

VIN1

ENB

1

3.3 V

250 mA

FAULT

TSD

VIN2

L1

33 μH

LX

FB1

Switch PWM

Control

Switch

Disable

Boot

Charge

10

FB2

VIN2

POR

Soft Start

Ramp Generator

Watchdog Timer

TSET

5V

0.1

ISEN

0.01

4.7

20

VIN1

750 kΩ

kΩ

kΩ

kΩ

4.7 kΩ

kΩ

kΩ

WDI

WDI

0.15 μF

μF

0.33

R3

10

R4

5.62

R

1

31.6

R2

9.76

GND

GND

μF

μF

μF

μF

μF

Pin-out Diagram

Terminal List Table

Number

Name

Function

1

TON

On time setting terminal

2

GND

Ground

3

FB2

4

VIN2

Input voltage 2

5

VO2

Regulator 2 output

6

WDI

Watchdog input

7

TSET

Soft start and watchdog timing capacitor terminal

8

NPOR

Fault output

9

FB1

10

POR

POR delay

11

ISEN

Current sense, limit setting for switching regulator, connect to GND

through series resistor

12

BOOT

Boot node for LX

13

LX

Switching regulator output

14

GND

Ground

15

VIN1

Input voltage 1

16

ENB

Enable input

–

PAD

Exposed thermal pad

TON

GND

FB2

VIN2

VO2

WDI

TSET

NPOR

ENB

VIN1

GND

LX

BOOT

ISEN

POR

FB1

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

PAD