RT8287

2

DS8287-03

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.

11

VCC

Bias Supply. Decouple with 0.1

μF to 0.22μF capacitor. The capacitance should

be no more than 0.22

μF.

12, 13

15 (Exposed Pad)

GND

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

GND for maximum power dissipation.

14

AGND

Analog Ground. Connect this pin to the system ground in PCB layout.

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

1.2V/3A

VIN

PGOOD

VCC

BOOT

FB

SW

9

8

1

2, 3, 4, 5

6

L

0.1µF

R1

R2

22µF

RT8287

11

SS

10

47nF

GND

12, 13, 15 (Exposed Pad)

EN

AGND

PGOOD

R3

100k

0.1µF

7

ON/OFF

14