A4403 データシートの表示（PDF） - Allegro MicroSystems

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A4403

Valley Current Mode Control Buck Converter

Allegro MicroSystems 

A4403

Valley Current Mode Control Buck Converter

Features and Benefits

▪ Extremely fast load-transient response with minimal

output voltage delta

▪ Achieves high step-down ratios with on-times < 50 ns

▪ User-configurable on-time, achieving switching

frequencies up to 2 MHz

▪ Minimal external components required

▪ Optimized for low value filter capacitors and inductors

▪ Wide input voltage range: 9 to 46 V

▪ Output Current: 3 A

▪ Low standby current <100 μA

▪ Supplied in thermally-enhanced QFN package

Applications:

▪ Printers, scanners

▪ Cable, DSL modems/routers

▪ Network and telecom

▪ Industrial control

▪ Distributed power systems

▪ Set top box

▪ High power LED supply

▪ Battery chargers

▪ GPS / Infotainment

Package 16-contact QFN (suffix EU):

4 mm × 4 mm × 0.75 mm

Description

The A4403 is a buck converter that uses valley current-mode

control. This control scheme allows very short switch on-times

to be achieved, making it ideal for applications that require

high switching frequencies combined with high input voltages

and low output voltages.

Low cost is accomplished through high switching frequencies

of up to 2 MHz, allowing smaller and lower value inductors

and capacitors. In addition, minimal external components are

required through high levels of integration. Optimal drive

circuits are utilized to minimize switching losses.

The switching frequency is maintained constant, as the on-time

is modulated by the input voltage. This feed-forward control

ensures excellent line correction. The on-time is set by an

external resistor pulled-up to the input supply.

When power is initially applied and the device is enabled, a

user-configurable soft-start function occurs to minimize inrush

current and to prevent output overshoot. Internal housekeeping

and bootstrap supplies are provided which only require the

addition of one small ceramic capacitor. A top-off charge pump

is also provide to ensure correct operation at light loads.

Internal diagnostics provide comprehensive protection against

overcurrents, input undervoltages, and overtemperatures.

The device package is a 16-contact, 4 mm × 4 mm, 0.75 mm

nominal overall height QFN, with exposed pad for enhanced

thermal dissipation. It is lead (Pb) free, with 100% matte tin

leadframe plating.

VIN

9 to 46 V

R1

100 kΩ

C1

2.2 μF

100 V

C5

47 nF

Typical Application Diagram

VIN

BOOT

LX

A 4403

TON

ISEN

DIS

C2

22 nF

L1

6.3 μH

R3

50 mΩ

D1

C3

10 μF

6.3 V

SGND

SS

FB

GND

VOUT

5.0 V

3A

C4

10 μF

6.3 V

R5

3.92 kΩ

R6

750 Ω

90.00

85.00

80.00

Efficiency versus Output Current

VIN = 42 V

5V

3.3 V

75.00

70.00

65.00

60.00

0

1

2

3

Output Current (A)

All capacitors are X5R or X7R ceramic

Resistors R3 and R4 should be surface mount, low inductance type, rated at 250 mW at 70°C

4403-DS, Rev. 1

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