RT9272

Preliminary

2

DS9272-09

August 2007

www.richtek.com

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

GND

Ground.

2

FB2

Feedback 2. Internal feedback voltage to set FB current of Ch2 as SP pin pull high.

3

CH2

Channel 2. Internal FB loop. Connect the cathode of LED to this pin.

4

VCC

Voltage Input Pin. Bypass a 2.2uF capacitor to GND to reduce the input noise.

5

CH1

Channel 1. Internal FB loop. Connect the cathode of LED to this pin.

6

FB1

Feedback 1. Internal feedback voltage to set FB current of Ch1 as SP pin pull low

7

EN

Chip Enable Pin. Pull low or floating this pin to disable the system. Using a PWM

signal on CE pin can achieve the dimming control.

8

OVP

Over Voltage Protection. Detect over voltage condition and latch system until SP, EN

or UVLO reset. Connect directly to the output capacitor.

9

SP

Selection Pin. Internal MOSFET selection. Pull low to turn on the internal Ch1. Pull

high to turn on Ch2. As SP input signal change, internal MOSFET of LX pin will turn

off 1ms to prevent the over voltage damage by the output voltage instant change.

10

LX

Switch Pin. Connect this pin to inductor and schottky diode. Minimize the track area

to reduce EMI.

Exposed Pad (11) NC

No Internal Connection.

Figure 1. 2LEDs for Sub panel and 4LEDs for Main panel

Note:

L : Measured by Murate LQH32C_53 series 4.7

μH with DCR = 0.15Ω

GND

CH1

RT9272

OVP

CH2

FB2

FB1

VCC

LX

EN

SP

Sub-Panel

Main Panel

V

IN

1

2

3

4

5

6

7

8

9

10

1uF

L

2.2uF

Chip Enable

C

OUT

DSH

SS0520

C

IN

R1

R2

4.7uF