RT8258

2

DS8258-02 March 2011

www.richtek.com

Function Block Diagram

Table 1. Recommended Component Selection

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

BOOT

Gate Driver Bootstrap Input Pin. Connect a 10nF or greater capacitor between PHASE

and BOOT pins to supply the MOSFET driver.

2

GND

Ground Pin. This pin should be connected to the (-) terminal of the output capacitor and

it should be kept away from the D1 and input capacitor for noise prevention.

3

FB

Output Voltage Feedback Input Pin. An external resistor divider from the output to GND

tapped to the FB pin sets the output voltage. The value of the divider resistors also set

loop bandwidth.

4

EN

Chip Enable (Active High). If the EN pin is open, it will be pulled to high by internal

circuit.

5

VIN

Power Supply Input Pin. Bypass VIN to GND with a suitable large capacitor to prevent

large voltage spikes from appearing at the input.

6

PHASE

Power Switching Output Pin. Connect this pin to the output inductor.

1.2V

1.5V

1.8V

2.5V

3.3V

5V

8V

10V

15V

R1 (k

Ω)

100

91

91

100

100

91

91

91

120

R2 (k

Ω)

200

100

75

47

32.4

17.4

10

7.87

6.8

L (

μH)

3.6

3.6

4.7

6.8

10

15

22

22

33

22

22

22

22

22

22

22

22

22

Note : The value of R1 is related to the loop bandwidth of the RT8258. It is strongly recommended to follow the

parameters in above table for the specific output voltage.

Driver

R

Q

S

Bootstrap

Control

+

-

Ramp

Generator

Oscillator

700kHz

+

-

PWM

Comparator

EA

Reference

Regulator

+

-

1.1V

1µA

+

-

400k

30pF

1pF

Shutdown

Comparator

OC Limit Clamp

Current Sense Amp

X20

BOOT

GND

FB

EN

VIN

PHASE

10k

3V

25mΩ