RT8280 データシートの表示（PDF） - Richtek Technology

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RT8280

3A, 24V, 3MHz Step-Down Converter

Richtek Technology 

RT8280

Typical Application Circuit

VIN

4.5V to 24V

Chip Enable

CIN

10µF

2 VIN

BOOT 1

7 EN

RT8280

SW 3

8 RT

RRT

24k

4,

9 (Exposed Pad)

GND

FB 5

COMP 6

CBOOT L

10nF 2.2µH

B330A

R1

31.6k

VOUT

3.3V/3A

COUT

22µF

CC

1.8nF

RC

24k

R2

10k

VOUT (V)

10

8

5

3.3

2.5

1.8

1.5

1.2

NCCP

Table 1. Recommended Component Selection for fSW = 2.2MHz

R1 (kΩ)

115

R2 (kΩ)

10

RC (kΩ)

68

CC (nF)

0.82

L (μH)

8.2

91

10

51

1

6.8

5 2.3

10

36

1.2

4.7

3 1.6

10

24

1.8

2.2

2 1.5

10

18

2.2

2

1 2.4

10

13

2.2

1.5

8 .87

10

12

2.2

1.5

4 .99

10

9

1.8

1

COUT (μF)

22

22

22

22

22

22

22

22

Functional Pin Description

Pin No.

1

2

Pin Name

BOOT

VIN

Pin Function

Bootstrap Power. BOOT supplies the drive for the high side N-MOSFET switch.

Connect a 10nF or greater capacitor from SW to BOOT to power the high side

switch.

Supply Input. VIN supplies the power to the IC, as well as the step-down

converter switches. Drive VIN with a 4.5V to 24V power source. Bypass VIN to

GND with a suitably large capacitor to eliminate noise on the input to the IC.

3

SW

4,

9 (Exposed Pad)

GND

5

FB

6

COMP

7

EN

8

RT

Switch Node. SW is the switching node that supplies power to the output.

Connect the output LC filter from SW to the output load. Note that a capacitor is

required from SW to BOOT to power the high side switch.

Ground. The exposed pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

Feedback Input. FB senses the output voltage to regulate. Drive FB with a

resistive voltage divider from the output voltage.

Compensation Node. COMP is used to compensate the regulation control loop.

Connect a series RC network from COMP to GND to compensate the regulation

control loop. In some cases, an additional capacitor from COMP to GND is

required.

Enable Input. EN is a digital input that turns the regulator on or off. Drive EN

higher than 1.4V to turn on the regulator, lower than 0.4V to turn off. For

automatic startup, leave EN unconnected.

Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the

switching frequency.

Copyright ©2012 Richtek Technology Corporation. All rights reserved.

www.richtek.com

2

is a registered trademark of Richtek Technology Corporation.

DS8280-02 March 2012

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