RT9271

2

DS9271-13 March 2007

www.richtek.com

Note : 1. D1 is Schottky diode (SS0520).

2. D2 ~ D4 are the WLED (HT-S91CW-DT) of HARVATEK.

3. LX is the SH4018 series of ABC TAIWAN ELECTRONICS CORP.

Recommended Circuits for Driving LEDs

Figure 1 to Figure 3 illustrates the recommended application circuits for driving white LEDs. The series connected LEDs

are driven with identical current to emit uniform luminescence, and the 250mV low reference voltage can minimize the

efficiency loss across the current-sensing resistor. The recommended current setting for driving white LEDs is 10mA to

20mA, and the dimming control can be implemented by toggling EN pin with 60Hz to 1kHz PWM clock. Please refer to

application notes for guidance of component selection and board layout.

Figure 3. RT9271 Drivers 3 Series WLEDs Application Circuit

Figure 2. RT9271 Drivers 2 Series WLEDs Application Circuit

VCC

EN

GND

LX

FB

Dimming

Control

C1

1uF

C3

1uF

D1

SS0520

LX

10uH

R2

12

OVP

D2

D3

V

IN

2.4 to 5V

VCC

EN

GND

LX

FB

Dimming

Control

C1

1uF

C3

1uF

D1

SS0520

LX

10uH

R2

12

OVP

D2

D4

D3

V

IN

2.4 to 6V

Typical AppIication Circuit

Figure 1. RT9271 Drivers 1 WLEDApplication Circuit

VCC

EN

GND

LX

FB

Dimming

Control

C1

1uF

C3

1uF

D1

SS0520

LX

10uH

D2

R2

12

OVP

V

IN

2.4 to 3.2V