RT8280 datasheet(2/16 Pages) RICHTEK

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RT8280

DS8280-02 March 2012

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Functional Pin Description

Pin No.

Pin Name

Pin Function

BOOT

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.

VIN

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.

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.

9 (Exposed Pad)

GND

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.

COMP

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.

Table 1. Recommended Component Selection for fSW = 2.2MHz

VOUT (V)

R1 (k

Ω)

R2 (k

Ω)

RC (kΩ)

C C (nF)

L (

μH)

COUT (μF)

115

0.82

8.2

6.8

52.3

1.2

4.7

3.3

31.6

1.8

2.2

2.5

21.5

2.2

1.8

12.4

2.2

1.5

8.87

2.2

1.5

1.2

4.99

1.8

Typical Application Circuit

4.5V to 24V

VIN

GND

BOOT

2.2µH

10nF

22µF

31.6k

10k

VOUT

3.3V/3A

10µF

Chip Enable

VIN

RT8280

B330A

RRT

24k

COMP

1.8nF

24k

9 (Exposed Pad)

CBOOT

COUT

CIN

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