RT8256

2

DS8256-01 March 2011

www.richtek.com

Functional Pin Description

Function Block Diagram

Pin No.

Pin Name

Pin Function

1

NC

No Internal Connection.

2

BOOT

High Side Gate Drive Boost Input. 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.

3

VIN

switches. Bypass VIN to GND with a suitable large capacitor to eliminate noise on the

input to the IC.

4

SW

Power Switching Output. 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.

5

GND

Ground.

6

FB

Feedback Input. FB senses the output voltage to regulate said voltage. The feedback

reference voltage is 1.222V typically.

7

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.

8

EN

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 it off. If the EN pin is open, it will be

pulled to high by internal circuit.

Table 1. Recommended Component Selection

R1 (k

Ω)

R2 (k

Ω)

L1 (

μH)

C

12

88.7

10

62

0.82

33

22

5

30

10

20

2.2

22

22

3.3

17

10

10

1.5

15

22

2.5

10.45

10

7.5

1.5

10

22

1.8

4.75

10

6

1.5

10

22

1.222

0

10

6

3.9

6.8

22

R

Q

S

Q

VA

+

-

+

-

+

-

+

-

EA

UV

Comparator

Oscillator

400kHz/120kHz

Foldback

Control

0.6V

Internal

Regulator

+

-

1V

1µA

Shutdown

Comparator

Current Sense

Amplifier

BOOT

VIN

GND

SW

FB

EN

COMP

1.222V

3V

10k

VA

Slope Comp

Current

Comparator

Gm = 780µA/V