LP3310-00

Jan.-2018

www.lowpowersemi.com

Page 6 of 9

Preliminary Datasheet

LP3310

Dimming control

a. Using a PWM Signal to EN Pin

For controlling the LED brightness, the LP3310 can

perform the dimming control by applying a PWM

signal to EN pin. The internal soft-start and wide

range dimming frequency from 100Hz to 100KHz can

insignificantly reduce audio noise when dimming.

The average LED current is proportional to the PWM

signal duty cycle. The magnitude of the PWM signal

should be higher than the maximum enable voltage

of EN pin, in order to let the dimming control perform

correctly.

VIN

EN

NC

LX

6

4

1

5

2

GND

LED+

VIN

4.7uH

C2

2.2uF

R1

12Ω

C1

10uF

LED-

PWM

R5

100KΩ

D1

b. Using a DC Voltage

Using a variable DC voltage to adjust the brightness

is a popular method in some applications. The

dimming control using a DC voltage circuit is shown

in below. According to the Superposition Theorem,

as the DC voltage increases, the voltage contributed

to VFB increases and the voltage drop on R2

decreases, i.e. the LED current decreases. For

example, if the VDC range is from 0V to 2.8V, the

selection of resistors in below sets dimming control

of LED current from 20mA to 0mA.

VIN

EN

NC

LX

6

4

1

5

2

GND

LED+

VIN

4.7uH

C2

2.2uF

R1

12Ω

C1

10uF

LED-

VDC

EN

R2

5.1KΩ

R3

68KΩ

R5

100KΩ

D1

c. Using a Filtered PWM signal

Another common application is using a filtered PWM

signal as an adjustable DC voltage for LED dimming

control. A filtered PWM signal acts as the DC voltage

to regulate the output current. The suggested

application circuit is shown in the below. In this circuit,

the output ripple depends on the frequency of PWM

signal. For smaller output voltage ripple (<100mV),

the recommended frequency of 2.8V PWM signal

should be above 2KHz. To fix the frequency of PWM

signal and change the duty cycle of PWM signal can

get different output current. According to the

application circuit of below, output current is from

35mA to 12mA by adjusting the PWM duty cycle from

10% to 90%.

VIN

EN

NC

LX

6

4

1

5

2

GND

LED+

VIN

4.7uH

C2

2.2uF

R1

12Ω

C1

10uF

LED-

PWM

EN

R2

6.8KΩ

R3

56KΩ

R4

100KΩ

C3

0.1uF

R5

100KΩ

D1