RT8055B

2

DS8055B-03 April 2011

www.richtek.com

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

SHDN/RT

Shutdown Control or Frequency Setting Input. Connect a resistor to ground from

device to be shut down.

2,

11 (Exposed Pad)

GND

Signal Ground. All small-signal components and compensation components should

be connected to this ground, which in turn connects to PGND at one point. The

exposed pad must be soldered to a large PCB and connected to GND for maximum

power dissipation.

3, 4

LX

Internal Power MOSFET Switches Output. Connect this pin to the inductor.

5

PGND

6

PVDD

Power Supply Input. Decouple this pin to PGND with a capacitor.

7

VDD

equal to PVDD.

8

PGOOD

Power Good Indicator. The pin is an open drain logic output that is pulled to Ground.

9

FB

Feedback Pin. This pin receives the feedback voltage from a resistive divider

connected across the output.

10

COMP

Error Amplifier Compensation Point. The current comparator threshold increases

with this control voltage. Connect external compensation elements to this pin to

stabilize the control loop.

Typical Application Circuit

Note : Using X5R/X7R Ceramic Capacitors

Table 1. Recommended Component Selsction

R1 (k

Ω)

R2 (k

Ω)

L1 (

μH)

3.3

75

24

30

0.47

2.2

22 x 2

2.5

51

24

27

0.47

2.2

22 x 2

1.8

30

24

22

0.47

2.2

22 x 2

1.5

21

24

18

0.47

2.2

22 x 2

1.2

12

24

15

0.47

1.0

22 x 2

1.0

6

24

13

0.47

1.0

22 x 2

22µF x 2

PVDD

LX

SHDN/RT

RT8055B

VDD

COMP

2µH

L1

10

3, 4

GND

FB

PGND

9

R1

R2

75k

24k

3.3V/3A

30k

470pF

22pF

R3

C1

R4

100k

6

7

PGOOD

22µF

5V

PGOOD

8

1

180k

2,11 (Exposed Pad)

5