RT8287A

2

DS8287A-03

June 2012

www.richtek.com

©

Copyright

2012 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Function Pin Description

Pin No.

Pin Name

Pin Function

1

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 21V power source. Bypass VIN to GND with a

suitably large capacitor to eliminate noise on the input to the IC.

2, 3, 4, 5

SW

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.

6

BOOT

High Side Gate Drive Boost Input. BOOT supplies the drive for the high side

N-MOSFET switch. Connect a 100nF or greater capacitor from SW to BOOT to

power the high side switch.

7

EN

Chip Enable (Active High). For automatic start-up, connect the EN pin to VIN with a

100k

Ω resistor.

8

FB

Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB

with a resistive voltage divider from the output voltage. The feedback threshold is

0.808V.

9

PGOOD

Power Good Output. The output of this pin is open-drain. Power good threshold is

90% low to high and 70% high to low of regulation value.

10

SS

Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from

SS to GND to set the soft-start period.

Typical Application Circuit

Table 1. Recommended Components Selection

R1 (k

Ω)

R2 (k

Ω)

L (

μH)

5

75

14.46

0

4.7

22 x 2

3.3

75

24.32

0

3.6

22 x 2

2.5

75

35.82

0

3.6

22 x 2

1.8

5

4.07

30

2

22 x 2

1.5

5

5.84

39

2

22 x 2

1.2

5

10.31

47

2

22 x 2

1.05

5

16.69

47

1.5

22 x 2

VIN

PGOOD

VCC

BOOT

FB

SW

9

8

1

2, 3, 4, 5

6

L

0.1µF

R1

R2

22µF

RT8287A

11

SS

10

47nF

GND

12, 13, 15 (Exposed Pad)

EN

AGND

PGOOD

R3

100k

0.1µF

7

ON/OFF

14

1.2V/4A