RT9301 datasheet(6/9 Pages) RICHTEK

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RT9301

DS9301-02

March 2007

www.richtek.com

Applications Information

The RT9301 is a 3-Channel current source driver for RGB

LED or white LEDs. The output current can be controlled

from 2mA to 50mA by adjusting the setting current from

external. It is easy to support a multi-color RGB LED.

Input UVLO

The input operating voltage range of the RT9301 is 2.8V to

5.5V. An input capacitor at the VIN pin could reduce ripple

voltage. It is recommended to use a ceramic 1uF or larger

capacitance as the input capacitor. This IC provides an

under voltage lockout (UVLO) function to prevent it from

unstable issue when startup. The UVLO threshold of input

falling voltage is set at 2.1V typically with a hysteresis

0.1V.

Output Current Setting

The LED current is setting by the current of ISET pin. The

LED current of the three channels (LED1, LED2, LED3)

could be set from the ISET (ISET1, ISET2, ISET3) pins

individually. The typical application circuit shows as

Figure 1.

Figure 1. Typical Application Circuit

The LED current can be controlled from an external voltage

(VSET) and a resistor (RSET) between VSET and ISET pin.

The voltage range of VSET is from 1.3V to 5.5V. The internal

reference voltage at ISET pin is 0.9V typically. LED current

is set as 800 times the current flowing into ISET pin.

Therefore, the LED current can be calculated as the

following equation.

LED3

LED2

LED1

GND

ISET1

BAT

VIN

ISET3

ISET2

SET3

SET2

SET1

RT9301

SET1

SET2

SET3

1uF

SET1

LED1

0.9V

800

For example, RSET1 = 45k

Ω and VSET1 = 1.8V, the current

of LED1 is equal to 16mA.

The LED current of each channel can be controlled from

2mA to 50mA. It is easy to obtain a multi-color output

by changing the current of ISET1, ISET2, and ISET3

respectively.

Figure 2 shows the characteristics of ILED vs. VSET. If the

RSET is selected, the LED current could be controlled from

VSET. The voltage of VSET must be higher than 1.3V to

enable the LED. For low LED current application, it is

recommended to use a higher resistance on RSET (for

example: RSET = 360k

Ω).

To disable the LED current, the ISET pin should be

connected to ground or floating. For one LED or two LEDs

application, the unused ISET pin should be connected to

GND. In addition, don

’ t short V

SETx to ISETx pin.

Figure 2. LED Current Setting

Figure 3. Application Circuit for Two LEDs

LED3

LED2

LED1

GND

ISET1

BAT

VIN

ISET3

ISET2

SET2

SET1

RT9301

SET1

SET2

1uF

1.5

2.5

3.5

4.5

5.5

VSET (V)

RSET = 36k

RSET = 51k

RSET = 75k

RSET = 160k

RSET = 360k

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