RT8259

2

DS8259-03 March 2011

www.richtek.com

Function Block Diagram

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

BOOT

Bootstrap. A capacitor is connected between PHASE and BOOT pins to form a floating

supply across the power switch driver. This capacitor is needed to drive the power switch‘s

gate above the supply voltage.

2

GND

Ground. This pin is the voltage reference for the regulated output voltage. For this reason,

care must be taken in its layout. This node should be placed outside of the D1 to C1 ground

path to prevent switching current spikes from inducing voltage noise into the part.

3

FB

Feedback. 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

Supply Voltage. Bypass VIN to GND with a suitable large capacitor to prevent large voltage

spikes from appearing at the input.

6

PHASE

Switch Output.

1.2

1.8

2.5

3.3

5

8

10

15

L1 (

μH)

2

2

3.6

4.7

6.8

10

10

15

R1 (k

Ω)

62

62

62

62

62

68

68

68

R2 (k

Ω)

124

49.9

29.4

19.6

12

7.5

5.9

3.9

Table 1. Recommended Component Selection, C2 = 22

μμμμμF

Driver

R

Q

S

Bootstrap

Control

+

-

Ramp

Generator

Oscillator

1.4MHz

+

-

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

Ω